Class 11 Medical Chemistry - The S-Block Elements

"$$Na^{+}$$ (cation) is smaller than $$Na$$ (atom)."
Answer whether the above statement is true or false.
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In the formation of cation, the radius of the cation is generally smaller than its atom. For Na, when it loses an electron, its outer shell will be removed thus having a smaller ionic radius. It will have a similar configuration to that of Neon.

The electronic configuration for Na atom is 2,8,1 (z=11) and electronic configuration for Na ion is 2,8 (z=10). There is a removal of the m shell and hence, the ion is smaller in size. After removal of one electron, the effective nuclear charge on sodium atoms increase due to which nucleus tends to attract the electrons with a greater force and thus, causing a shrink in size.

Hence, the statement is correct and correct answer is 1.

Out of $$Be^{2+} $$, $$Mg^{+}$$ and $$Ca$$, $$Be^{2+} $$ has maximum IE.
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The ionization energy (IE) of the element M is a measure of the energy required to remove one electron from one mole of the gaseous atoms M. IE is affected by size, effective nuclear charge, type of orbital from which the electron is being removed and electronic configuration. So, it decreases while moving down the group.

Be, Mg, and Ca belong to the second group of the periodic table. All of them can lose 2 electrons to attain a stable state. So, Be being the smallest of all has the maximum IE. Also, when it loses 2 electrons to become $$Be^{2+}$$, energy required to remove 1 more electron after achieving the stable state is very high. Mg, when loses 1 electron to become $$Mg^+$$, its size decreases so, the 2^nd IE required to remove 1 more electron is higher. Ca has the lowest IE as its size is bigger as compared to the other two and also, it has 2 electrons to lose to achieve a stable state.

Hence, the statement is correct.

The single-bonded metallic radius of sodium is $$157$$ pm. Assume that the increment between radii of different magnitudes is $$60$$ pm.The van der Waals' radius $$Na$$ in pm is $$(209 + x)$$. Find value of $$x$$.

Metallic radius is smaller than van der Waals' radius.

The single-bonded metallic radius of sodium is $$157$$ pm.

The increment between radii of different magnitudes is $$60$$ pm.

The van der Waal's radius of $$Na$$ in pm is $$157 + 60= 217\ pm$$

$$209+x=217$$

$$ \Rightarrow Hence, x= 8$$

Hydration energy of $$Mg^{2+}$$ is more than $$Li^{+}$$.
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The heat energy released when new bonds are made between the ions and water moleculesis known as the hydration enthalpy of the ion. The hydration enthalpy is the enthalpy change when 1 mole of gaseous ions dissolve in sufficient water to give an infinitely dilute solution. Hydration enthalpies are always negative. Larger the atomic size lesser the hydration energy or the energy decreases.

The size of $$Li^{+}$$ greater than $$Mg^{2+}$$.So, the hydration energy of $$Mg^{2+}$$ is greater than $$Li^{+}$$.So, the correct order of hydration energy is $$Mg^{2+}\, >\, Li^{+}$$.

"Na and Mg are also called bridge element since it links Group IA and Group IB".

State whether the above statement is true or false.

Na is called bridge element since it links Group IA and Group IB.

Mg is called bridge element since it links group IIA and IIB.

Hence,statement is true.

Compare Oxidation state of Li and Be.

Oxidation state of Li is +1 since it is an alkali metal and has 1 electron in its outermost shell which it can loose easily.

Oxidation state of Be is +2 since it is an alkaline earth metal and has 2 electrons in its outermost shell which it can loose easily.

Chlorophyll a biologically important molecule in which magnesium atoms are held in a position by organic groups.
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Chlorophyll (also chlorophyl) is a term used for several closely related green pigments found in cyanobacteria and the chloroplast of algae and plants . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to absorb energy from light.
Chlorophyll is a chlorin pigment, which is structurally similar to and produced through the same metabolic pathway as other pophyrin pigments such as heme. At the center of the chlorine ring, is a magnesium ion.
Hence, option 1 is correct.

On heating carbonates of Li and Mg, what product will be formed?

On heating carbonates of Li and Mg both decompose to form $$CO_2$$ and their respective oxide.

$$Li_2CO_3 \xrightarrow {heat} Li_2O + CO_2$$

$$MgCO_3 \xrightarrow {heat} MgO + CO_2$$

(a) Describe how the following properties vary on descending group IA and IIA (alkali and alkaline earth metals) and state how these properties differ between the two groups?
(i)$$(IE)_1 and (IE)_2$$
(ii) cationic radii
(iii) rates of reaction with cold water
(b) For the same s-block elements, discuss:
(i) the action of heat on their nitrates
(ii) the crystal structures of their chlorides, XY type only.

i) Ionization Energy decreases down the group.

$$IE_1$$ for IA > $$IE_1$$ for IIA

$$IE_2$$ for IA < $$IE_2$$ for IIA because after losing 1 electron 1A elements aquire noble gas configuration and therefore a very high ionization energy is required to remove the 2nd electron as compared to IIA elements.

ii)Cationic radii increases down the group and decreases along the period.

iii)The Group 1 and 2 metals become more reactive towards water as you go down the Group.

i)Nitrates of alkali metals, except LiNO₃, decompose on strong heating to form nitrites.

2KNO_{3 (s)} → 2KNO_2(s) +O_2(g)

LiNO₃, on decomposition, gives oxide.

2LiNO_3(s) Li₂O_(s) + 2 NO_2(g) + O_2(g)

Similar to lithium nitrate, alkaline earth metal nitrates also decompose to give oxides.

2Ca(NO₃)_(s) 2CaO_(s) + 4 NO_2(g) + O_2(g)

As we move down group 1 and group 2, the thermal stability of nitrate increases.

ii) The alkali halides crystallize in the NaCl structure also known as rock-salt structure (rock salt is the mineral form of sodium chloride); exceptions being CsCl, CsBr, and CsI, which crystallize in the CsCl structure. In the NaCl structure (face-centered cubic lattice), each cation is surrounding by six anions, and vice versa (coordination number of 6). In the CsCl structure, each cation is surrounded by eight anions and vice versa (coordination number of 8).

Consider the following statement:
Both $$Li$$ and $$Mg$$ forms hydrated chloride.
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The statement is true.

Both $$Li$$ and $$Mg$$ forms hydrated chloride i.e $$LiCl.2H_2O$$ and $$MgCl_2.6H_2O$$ respectively while other elements of gorup I and II forms anhydrous chloride.

Chlorides of both Li and Mg are deliquescent (absorb moisture from surroundings) and soluble in alcohol and pyridine.They separates out from aqueous solutions as hydrated crystals.

State whether the given statement is true or false:

"The polarizing power of $$Li^{+}$$ is greater than $$Na^{+}$$."

Neutral nonpolar species have spherically symmetric arrangements of electrons in their electron clouds. When in the presence of an electric field, their electron clouds can be distorted. The ease of this distortion is defined as the polarizability of the atom or molecule.

A cation is more polarising if it has a higher charge or a smaller size or both (higher “charge density”). Among Li+ and Na+; Li+ is more polarising than Na+ (Li is smaller, higher up the group) .

Explain, why electronegativity of Li is greater than Mg?

Electronegativity of an element is its tendency to attract bond pair electrons.

The electronegativity of Li and Mg can be understand by their electronic configuration as follows-

$$Li: 1s^2\ 2s^1$$

$$Mg: 1s^2\ 2s^22p^6\ 3s^2$$

Li has 1 electron in its valence shell (n=2). However, Mg has 2 electrons in its valence shell (n=3). The valance shell of Li is closer than that of Mg which makes Li more electronegative than Mg.

"The tendency of Li and Mg to form nitrides is such that Li forms nitride whereas Mg does not."
Answer whether the above statement is true or false.
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The statement is false.

Both $$Li$$ and $$Mg$$ form nitrides; $$Li_3N$$ and $$Mg_3N_2$$ respectively.

Lithium is the only alkali metal (group 1) to form a nitride when burnt in air. (This is however common with the alkaline earth metals (group 2).

Because $$Li_3N$$ is covalent and as the metallic character increases ,the tendency of donating electron and forming ionic bond increases due to which, strength of metal nitrogen bond decreases.

"$$LiCl$$ is covalent while $$NaCl$$ is ionic."
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The electronic configuration of $$Li^+$$ is $$1s^2$$. We know from the Schrödinger Wave Equation that the 1s Atomic Orbital is close to the nucleus and as result of the +3 charged nucleus, the $$Li^+$$ ion is anomalously small. Because of the high charge density (charge over radius), the $$Li^+$$ ion is able to polarize (distort) the electron cloud of neighboring anions. This is equivalent to saying that $$Li^+$$ salts have more covalent character. According to Fajan's rules $$Na^+$$ has a ionic radius of ~116 pm and the polarizing power is significantly less so there is less covalent character (but not zero) in $$NaCl$$. Therefore $$LiCl$$ is covalent while $$NaCl$$ is ionic.

Hence, the statement is true.

"Both Li and Mg forms Basic oxides."
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All alkali metal oxides form basic solutions of hydroxides when dissolved in water.

$$Li_2O+ H_2O \rightarrow 2 LiOH $$

Most group 2 oxides and hydroxides are only slightly soluble in water and form basic, or alkaline solutions of hydroxides.

$$MgO + H_2O \rightarrow Mg(OH)_2$$

Match the classification (in List I) with the element (in List II).

(A) Magnesium $$(Mg)$$ with atomic number $$12$$, is an alkaline earth metal.
(B) Francium $$ (Fr) $$ with atomic number $$87$$ is an alkali metal. It is radioactive.
(C) $$Rb $$ with atomic number $$37$$ is an alkali metal.
(D) Arsenic $$ (As) $$ with atomic number $$33$$ is a metalloid.

"Li metal is used in photoelectric cells, while Cs is not used."
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When exposed to light, the alkali metals lose electrons. This is known as photoelectric effect. Electrons of lithium are strongly held by nucleus as Li is smaller in size and therefore, requires high energy to lose an electron. While on the other hand, Cs has low ionization energy. Hence, it can easily lose electrons and cannot be utilized in photoelectric cells.

Hence, the correct answer is 1.

"Lithium is the only metal among alkali metals that can form nitride."
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The statement is correct.

$$N^{3-}$$ is very small in ionic size and thus, can be set into crystalline lattice with smaller $$Li^{+}$$ ion. Thus, $$Li_3N$$ is formed.

$$6Li\, +\, N_2\, \rightarrow\, 2Li_3N$$

Other alkali metals donot form nitrides due to larger size.

"Polarising power of $$Li^{+}$$ ion is nearly the same as that of $$Mg^{2+}$$ ion."
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It has been seen that Li differs from other alkali metal in many respects and shows a close resemblance to Mg (diagonal relationship), the second element of group-2 and diagonally opposite to Li in the periodic table. On moving diagonally in the periodic table, the polarising power i.e. ratio of the ionic charge and square of the ionic radius is nearly same for the Lithium and Magnesium (ionic charge and ionic radius of Li and Mg are +1 and +2 and 60pm and 65pm respectively) and accounts for the similarities between the properties of the two elements.

"When aqueous $$KO_2$$ solution reacts with $$CO_2$$, $$O_2$$ is formed and thus, $$KO_2$$ is used in submarines."
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When aqueous $$KO_2$$ solution reacts with $$CO_2$$, $$O_2$$ is formed and thus, $$KO_2$$ is used in submarines.

$$4KOH + 2CO_2 \longrightarrow K_2CO_3 +3O_2$$

Potassium superoxide is used as a $$CO_2$$ scrubber, $$H_2O$$ dehumidifier and $$O_2$$ generator in rebreathers, spacecraft, submarines and spacesuit life support systems.

"Carnallite is $$KCl\, \cdot\, MgCl_2\, \cdot\, 6H_2O$$."

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Carnallite is an evaporite mineral, a hydrated potassium magnesium chloride with formula KMgCl36(H2O). It is variably colored yellow to white, reddish, and sometimes colorless or blue.

"Li of group IA and Be of group IIA show diagonal relationship."
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Li shows diagonal relationship with Mg and not Be.

A diagonal relationship is said to exist between certain pairs of diagonally adjacent elements in the second and third periods of the periodic table. These pairs lithium (Li) and magnesium (Mg), beryllium (Be) and aluminium (Al), boron (B) and silicon (Si) etc. exhibit similar properties.

Such relationship occurs because crossing and descending the periodic table have opposite effects. On moving across a period of the periodic table, the size of the atoms decreases, and on moving down a group the size of the atoms increases. Similarly, on moving across the period, the elements become progressively more covalent, less basic and more electronegative, whereas on moving down the group the elements become more ionic, more basic and less electronegative. Thus, on both descending a group and crossing the period by one element, the changes "cancel" each other out, and elements with similar properties which have similar chemistry are often found – the atomic size, electronegativity, properties of compounds (and so forth) of the diagonal members are similar.

"The lattice energies of alkaline earth metal salts are much higher than these of alkali metal salts."
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The salt with the smaller cation has the higher lattice energy. Alkaline earth metals are smaller in size than respective earth metals of their period and therefore, have higher lattice energies. Higher lattice energies cause the alkaline earth metals to be more reactive than the alkali metals toward group 15 elements.

The alkali metals follow the noble gases in their atomic structure. What properties of these metals can be predicted from this information?

To attain noble gas configuration, alkali metals loose 1 electron easily to become cations. So, it can be predicted that they are electropositive and have low values of ionization energy

"$$Be$$ and $$Al$$ are made passive by $$HNO_3$$."
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$$Be$$ and $$Al$$ are made passive by $$HNO_3$$.

When they comes into contact with nitric acid, an impervious layer of oxide is formed. This layer of aluminium oxide and beryllium oxide will prevent the nitric acid from coming into contact with the inner metal. Thus, this layer protects and prevents further reaction.

"Li of group IA and Mg of group IIA show diagonal relationship."
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Due to small size of lithium, it differs from other alkali metals but resembles Mg as its size is closer to Mg, its resemblance with Mg is known as diagonal relationship. Generally, the periodic properties shows either increasing or decreasing trend along the group and vice versa along the period which brought the diagonally situated elements to closer values.

Period Group I Group II

2 Li Be

3 Na Mg

"Of the alkali metals, only Na forms nitrides."
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Of the alkali metals, only $$Li$$ forms nitrides. This is because of lattice energies that only lithium forms a stable oxide and nitride.

When Lithium reacts with nitrogen gas at room temperature $$(N_2)$$, it forms Lithium Nitride $$(Li_3N)$$ which is stable because the lattice energy released from the formation of $$Li_3N$$ is high enough to make the overall reaction exothermic. For other alkali metals (Na, K, Rb, Cs), the lattice energy for the $$M_3N$$ crystal is progressively lesser, and therefore, these compounds are highly unstable or do not form at all.

"The enthalpy of hydration decreases in going from $$Li^{+}$$ to $$Cs^{+}$$."
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The enthalpy of hydration decreases in going from $$Li^+ \ to \ Cs^+$$.

The heat energy released when new bonds are made between the ions and water molecules is known as the hydration enthalpy of the ion.

Smaller the ion, greater is the charge density and hence, more is the extent of hydration. The hydration enthalpies of alkali metal ions therefore, decrease with increase in ionic size. The magnitude of hydration energy is directly proportional to charge and inversely proportional to radius of ion.

$$ Li^+ > Na^+ > K^+ > Rb^+ > Cs^+$$

"$$KO_2$$ is $$O_2$$ absorber and $$CO_2$$ producer." It is also used in submarines."
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$$KO_2$$ is $$CO_2$$ absorber and $$O_2$$ producer.

It is also used in submarines as it absorbs $$CO_2$$ and increases oxygen content as follows :

$$4KO_2 + 2CO_2 \longrightarrow 2K_2CO_3 + 3O_2$$

Compare the solubility and thermal stability of alkali metals carbonates with those of the alkaline earth metals nitrates.

Thermal stability ofAlkaline earth metal nitrate ---Alkaline earth metal nitrate decompose on heating.All alkaline earth metals Nitrates decompose to form metal oxide, $$NO_2$$ and $$O_2$$.

Thermal stability of alkali metal carbonate---- alkali metals carbonates are stable and do not decompose even at high temperature.

solubility of alkaline earth metal nitrates --Nitrates, of alkaline earth metals are soluble in water.thier solubility, however decreases as we move down the group because their hydration energies decreases more rapidly than the lattice energies.

Solubility of alkali metal carbonates ----alkali metals carbonates are soluble in water. Their solubility however increases as we move down the group since the lattice energies decreases more rapidly than the hydration energies.

"Be and Al doesnot show diagonal relationship."
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$$Be$$ and $$Al$$ show diagonal relationship."

A diagonal relationship is said to exist between certain pairs of diagonally adjacent elements in the second and third periods of the periodic table. These pairs iclude (lithium (Li) and magnesium (Mg), beryllium (Be) and aluminium (Al), boron (B) and silicon (Si). Such relationship occurs because crossing and descending the periodic table have opposite effects. On moving across a period of the periodic table, the size of the atoms decreases and on moving down a group, the size of the atoms increases. Similarly, on moving across the period, the elements become progressively more covalent, less basic and more electronegative, whereas on moving down the group, the elements become more ionic, more basic and less electronegative. Thus, on both descending a group and crossing the period by one element, the changes "cancel" each other out, and elements with similar properties which have similar chemistry are often found – the atomic size, electronegativity, properties of compounds (and so forth) of the diagonal members are similar.

"$$Li_3N$$ is decomposed by water forming $$NH_3$$ gas."
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$$Li_3N$$ is decomposed by water forming $$NH_3$$ gas.

$$Li_3N + 3H_2O \longrightarrow 3LiOH + NH_3$$

This property shows diagonal relationship with $$Mg$$.

"When sodium metal is exposed to atmosphere, it reacts with air and forms sodium hydroxide film which absorbs $$CO_2$$ from air and forms sodium bicarbonate."
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Sodium is ordinarily quite reactive with air and the reactivity is a function of the relative humidity or water-vapour content of the air.

The corrosion of solid sodium by oxygen also is accelerated by the presence of small amounts of impurities in the sodium. In ordinary air, sodium metal reacts to form a sodium hydroxide film, which can rapidly absorb carbon dioxide from the air, forming sodium bicarbonate.

$$Na^{+}$$ is coloured.

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$$Na^+$$ is white in colour.

The electronic configuration of $$Na^+$$ is $$1s^2 2s^2 2p^6 $$ and in excited state, it is $$1s^2 2s^2 2p^5 3s^1$$.
In order to absorb visible light, an electron would have to move to a higher energy orbital . The difference in energy of the orbitals would have to equal the energy of a visible wavelength photon. For p orbital to s orbital shift, a much higher energy is needed and would correspond to UV light. Since there is no absorption of visible light, $$Na^+$$ ion is white and gives colourless aqueous solution.

"$$Ca_3(PO_4)_2$$ is the primary constituent of teeth and bones."
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$$Ca_3(PO_4)_2$$ is the primary constituent of teeth and bones.

It is insoluble non-acid calcium salt of orthophosphoric acid. It occurs in bones and is the main constituent of bone ash.

The inorganic part of hard tissues (bones and teeth) of mammals consists of calcium phosphate, mainly of apatitic structure.

"The chief factor responsible for the anomalous behavior of lithium is its small size."
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Anomalous behavior of lithium is due to extremely small size of lithium. Its cation on account of small size and high nuclear charge exerts the greatest polarizing effect out of all alkali metals on negative ion. Consequently, lithium ion possesses remarkable tendency towards solvation and develops covalent character in its compounds. The ability to form covalent bond due to high electropositive character and the polarising power of $$Li^+$$ is comparable to that of magnesium ion. The $$Li^+$$ ion has a charge to size ratio comparable to that of $$Mg^{2+}$$, and hence, the properties of some lithium compounds resemble those of magnesium compounds.

"Be is not readily attacked by acids due to formation of oxide layer."
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$$Be$$ is not readily attacked by acids due to formation of oxide layer.

The surface of beryllium metal is covered with a thin layer of oxide that helps protect the metal from attack by air. It does not oxidize in air even at $$600^{o}C$$.

$$2Be + O_2 \longrightarrow 2BeO$$

"The thermal stability of group II oxysalts is more than those of the group I oxysalts."
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The thermal stability of group II oxysalts is less than those of the group I oxysalts.

The thermal stability of the oxysalts rises with the increase in electropositivity of the metal and so, it increases down the group and decreases along the period.

Lithium is the only alkali metal to form a nitride directly.

Write the chemical equation.

Lithium is the only alkali metal to form a nitride directly.
$$6Li+N_2 \rightarrow 2Li_3N$$
In this behaviour, $$Li$$ is similar to $$Mg$$.

"Potash magnesia is $$K_2SO_4 . MgSO_4 . 6H_2O$$."
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Potash magnesia is $$K_2SO_4 . MgSO_4 . 6H_2O$$.

Its commercial name is K-Mag.

Compare the chemistry of group 1 metals with that of group 2 metals with respect to the following:
Solubility of carbonates improves on going from group 1 to group 2.

Carbonates formed by alkali metals are very stable compared to those formed by alkaline earth metals. Carbonates of alkaline earth metals decompose easily upon heating.

The carbonates become less soluble down the group. All the Group 2 carbonates are very sparingly soluble. Magnesium carbonate, for example, has a solubility of about 0.02 g per 100 g of water at room temperature.

There is little data for beryllium carbonate, but as it reacts with water, the trend is obscured. The trend to lower solubility is, however, broken at the bottom of the group: barium carbonate is slightly more soluble than strontium carbonate.

Compare and contrast the chemistry of group 1 metals with that of group 2 metals with respect to the following:

Polarizing power of cations increases on going from group 1 to group 2.

Ionic radius increases down the group reducing the polarizing power of the cation.group 2 metal are less stable than group 1 because they have a smaller ionic radius .

The polarizing power and polarizability which enhances the formation of covalent bonds is favoured by the following factors:

Small cation: the high polarizing power stems from the greater concentration of positive charge on a small area. This explains why LiBr is more covalent than KBr.

Large anion: the high polarizability stems from the larger size where the outer electrons are more loosely held and can be more easily distorted by the cation. This explains why for the common halides, iodides, are the most covalent in nature .

Sodium is found more useful than potassium. If true enter 1,if false enter 0.

Sodium serves almost all purposes where potassium in needed.
Sodium is cheaper than potassium. Hence, sodium is more usefull than potassium.

Compare and contrast the chemistry of group 1 metals with that of group 2 metals with respect to oxides.

Group 1 oxides are more basic than group 2 oxides because group 1 oxides form strong base than group 2 oxides on reaction with water.

$$MgO+H_2O \rightarrow Mg(OH)_2$$

$$Na_2O+H_2O\rightarrow 2NaOH$$

Explain how does the melting point change on moving from group-1 to group-2 in the periodic table?

The melting points is the amount of energy required to break a bond (s) to change the solid phase of a substance to a liquid.

Generally, stronger the bond between the atoms of an element, the more energy required to break that bond. Because temperature is directly proportional to energy, a high bond dissociation energy correlates to a high temperature.

Melting points are varied and do not generally form a distinguishable trend across the periodic table. However, metals generally possess a high melting point. Melting point increases on moving from group 1 to group 2 in the periodic table.

Why are sodium and potassium kept in kerosene oil ?

$$Na$$ and $$K$$ are very reactive metals and kept in kerosene oil to prevent it from coming in contact with oxygen and moisture as they react to form their hydroxides. This is an exothermic reaction and lot of heat is generated so both the metals are kept in kerosene oil.

What is the most common oxidation state of alkali metals?

The most common oxidation state of alkali metals is +1. The outer electronic configuration of alkali metals is $$ns^1$$.

They can lose this electron readily to form a unipositive ion with stable noble gas configuration.

So, the correct answer is 1

Match the column.

A.From the periodic table, Li is the first element of group - I which has ns1 configuration.Smaller the cation, greater is the degree of hydration.It is a fact that Li+ has greatest reducing nature in aqueous medium due to maximum hydration energy for Li+ ion.
B.From the periodic table, atomic number of Na is 11 and has ns1 configuration
C.K also comes under group - I which has ns1 configuration
D.It comes under radiactive elements group in the periodic table

Statement: Barium sulphate is sparingly soluble in water whereas beryllium sulphate is freely soluble.

Enter 1 if the given statement is true if false enter 0

$$\begin{matrix}BaSO_4 (Barium\, sulphate) &BeSO_4 \\ H.E < L.E &H.E > L.E \end{matrix}$$

Hydration energy of barium sulphate is less than its lattice energy and hydration energy of beryllium sulphate is more than its lattice energy. Therefore, barium sulphate is insoluble and beryllium sulphate is freely soluble.

Hence, the given statement is $$\text{false}$$ and correct entry is $$0$$

Write the word equation and the chemical equation for Magnesium ribbon burned in air.

$$Word\ equation :$$Magnesium (Mg) + Oxygen $$(O_2)\, \rightarrow$$ Magnesium oxide (MgO)

$$Chemical\ equation: 2\, Mg\, +\, O_2\, \rightarrow 2\, MgO$$

It is undoubtedly a chemical change because Magnesium(s) burn in air and converts to Magnesium (II) Oxide.

Alkaline earth metals have higher melting points than alkali metals.
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Alkaline earth metals have higher melting points than alkali metals. They have two electrons in their valence shell resulting in the formation of strong metallic bonds for atom binding in the metal crystal lattice. On the other hand, alkali metals have only one electron in their outermost shell.

Metallic bonding is much stronger in alkali metals compared to alkaline earth metals.
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All of the elements of group two i.e. alkaline earth metals have two electrons in their outer shell. Metallic bonds in the alkaline earth metals are thus, stronger than for the alkali metals, resulting in higher melting points, but they are still quite reactive because the two outer electrons are easily lost.

The hydroxides and carbonates of sodium and potassium are easily soluble in water while the corresponding salts of magnesium and calcium are sparingly soluble in water. Explain?

The atomic/ionic size of Na and K is larger than that of Mg and Ca.
Hydroxides and carbonates of Na and K have lower lattice enthalpies than those of Ca and Mg. This results in high solubility for hydroxides and carbonates of Na and K whereas those of Mg and Ca are sparingly soluble.

Why are potassium and caesium used, rather than lithium used in photoelectric cells?

The ionization potentials of potassium and cesium are lower than that of lithium. On exposure to light, potassium and caesium easily emit electrons however lithium does not. Hence, potassium and caesium are used in the photoelectric cell.

Why are lithium salts commonly hydrated and those of the other alkali ions usually anhydrous?

Among alkali metal ions, Li(I) has smallest size due to which it can easily polarize water molecules. Li salts get bonded to water of crystallization. The lithium chloride contains 2 water molecules per mole of LiCl. The other alkali metals being bigger in size cannot easily polarize water molecules. Hence, there salts do not get bonded to water of crystallization.

Beryllium and magnesium do not give colour to flame whereas other alkaline earth metals do so. Why?

Be and Mg have small atomic size and high ionization energies when compared to other alkaline earth metals. The energy of flame is not sufficient to excite the electrons of Be and Mg to higher energy level. Hence, Be and Mg do not give any color in Bunsen flame.

Explain why can alkali and alkaline earth metals not be obtained by chemical reduction methods?

Alkali and alkaline earth metals have high reduction potentials. Hence, they are very strong reducing agents. Hence, other reducing agents cannot reduce oxides or other compounds of alkali and alkaline earth metals. Hence, chemical reduction is not possible.

Beryllium doesnot exhibit covalency beyond 4.
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Beryllium does not exhibit a covalency beyond 4.

Beryllium does not exhibit coordination number more than four as it has four orbitals in the valence shell. The other members of this group has coordination number 6 due to the presence of d orbitals.

Write reactions to justify amphoteric nature of aluminium.

Aluminium is amphoteric in nature as it reacts with acids as well as alkalies.

$$\displaystyle 2Al+6HCl \rightarrow 2Al^{3+} + 6Cl^-+3H_2$$

$$\displaystyle 2Al+2NaOH+6H_2O \rightarrow 2Na[Al(OH)_4]^-+3H_2 $$

Identify the diagonal neighbours in the periodic table.

A diagonal relationship is said to exist between certain pairs of diagonally adjacent elements in the second and third periods of the periodic table.

It is found that the chemistry of a first-row (second period) element often has similarities to the chemistry of the second-row (third period) element being one column to the right of it in the periodic table.

Thus, the chemistry of Li has similarities to that of Mg, the chemistry of Be has similarities to that of Al, and the chemistry of B has similarities to that of Si.

These are called diagonal relationships.

Calcium floats over water during its reaction with water. Give reason.

Hydrogen gas is obtained during the reaction of calcium with water.
$$\displaystyle Ca+2H_2O \rightarrow Ca(OH)_2 +H_2 \uparrow $$
This hydrogen gas is adsorbed on the surface of calcium. Hence, calcium floats over water during its reaction with water.

Identify the following substances which are underlined:
An alkaline gas which produces dense white fumes when reacted with hydrogen chloride gas.

Ammonia is an alkaline gas. It reacts with hydrogen chloride to form ammonium chloride. Dense white fumes obtained are of ammonium chloride.

What is the number of products formed on heating nitrates of lithium and magnesium?

$$4LiNO_3 \longrightarrow 2Li_2O + 4NO_2 + O_2$$

$$2Mg(NO_3)_2 \longrightarrow 2MgO + 4NO_2 + O_2$$

In each case, there are 3 products formed.

Write any two biological importance of Magnesium.

Biological importance of magnesium-

Main component of chlorophyll(photosynthesis)
Responsible for stability and proper functioning of genetic material
Maintain electrolyte balance in body
Regulate the functions of enzymes
Helps to from the ATP.

Mention any three diagonal relationship similarities between Berylium and Aluminium.

Diagonal relationships between Beryllium and Aluminium

Both metals have the tendency to form covalent compounds
Both $$BeCl_2$$ and $$AlCl_3$$ act as Lewis acids and are used as Friedel craft catalyst
Both elements have the same electronegativity and polarising power
Both $$BeCl_2$$ and $$AlCl_3$$ have chlorine bridged structures in vapour phase.

Comment on the existance of $$Be_2$$.

Be has electronic configuration$$1s^2,2s^2$$and s orbital is completely filled and doesn't require any electron to complete its orbital.

In $$Be_2$$ the total number of bonding electron is equal to total number of antibonding electron.

Hence,$$Be_2$$ doesn't exist at all.

Thus , lithium shows similarities to magnesium and beryllium to aluminium in many of their properties. This type of diagonal similarity is commonly referred to as diagonal relationship in the periodic table. The diagonal relationship is due to the similarity in ionic sizes and / or charge / radius ratio of the elements.

Beryllium $$(Be)$$ shows resemblance with its diagonally opposite element Aluminium $$(Al)$$.

Similarities are:

(1) Both metals have a tendency to form covalent compounds. Example: The chlorides of both being covalent are soluble in organic solvents.

(2) These two elements have same electronegativity and the polarising power i.e. charge/ radius ratio of their ions are very similar.

(3) Both $$BeCl_2$$ and $$AlCl_3$$ act as Lewis acid.

(4) Both metals dissolve in strong alkalies to form soluble complexes.

(5) The oxides of both $$Be(BeO)$$ and $$Al(Al_2O_3)$$ are hard, high melting insoluble solids.

$$BeO$$ is almost insoluble but $$BeSO_{4}$$ is soluble in water. Explain.

$$BeO$$ is almost insoluble in water and $${ BeSO }_{ 4 }$$ is soluble in water because $${ Be }^{ 2+ }$$ is a small cation with high polarising power and $${ O }^{ 2- }$$ is a small anion. When BeO is dissolved in water, the hydration energy of its ions is not sufficient to overcome the high lattice energy. Thus, $$BeO$$ is insoluble in water

Lithium differs from other elements of the group. Why?

Lithium is hard, has high electronagitivity, high ionisation potential, high melting as well as boiling point, lithium hydride are stablest hydrides, it is the only alkali metal which can react with nitrogen to form nitride, due to its small size it forms covalent compounds,it shows diagonal relationship with beryllium.

Name the three metals which react with cold water to form hydrogen gas. Support your answer with equally balanced chemical equations.

$$Na,K,Rb$$ reacts readily with water to form hydrogen gas & corresponding hydroxide.

$$2Na+2H_2O \longrightarrow 2NaOH+H_2 \uparrow$$

$$2K+2H_2O \longrightarrow 2KOH+H_2 \uparrow$$

$$2Rb+2H_2O \longrightarrow 2RbOH+H_2 \uparrow$$

Write any four differences between Lithium and other alkali metals.

$$Li$$ on heating with $$NH_3$$ forms $$Li_3N$$ whereas $$Na$$ does not form $$Na_3N$$. Explain.

$$Li$$ in heating with $${ NH }_{ 3 }$$ from $${ Li }_{ 3 }N$$ but $$Na$$ does not form $${ Na }_{ 3 }N$$. $$Na$$ on reaction $${ NH }_{ 3 }$$ forms sodamide $$\left( { NaNH }_{ 2 } \right) $$.

$$6Li+2{ NH }_{ 3 }\longrightarrow 2{ Li }_{ 3 }N+3{ H }_{ 2 }$$

$$2Na+2{ NH }_{ 3 }\longrightarrow 2{ NaNH }_{ 2 }+{ H }_{ 2 }$$

(a)Licl is hydrated, but NaCl is always anhydrous. Why ?
(b) Why is it that although $$L{i^ + }$$ is far smaller than the othe metals ions, it moves through a solution less rapidly than the others ?

Hydration energy is inversely proportional to the size. Size of $$Li^+$$ is smaller than the $$Na^+$$so hydration energy of lithium is greater than that of sodium so LiCl is hydrated while NaCl is anhydrous.

The positive charge density around $$L{i}^{+}$$ion is quite high due to its very small size. It can attract several layers of water molecules and gets highly hydrated. Thus, $$L{{i}^{+}}$$ion is bigger in size compared with other alkali metal ions which are less hydrated. As a result, it moves through the aqueous solution less rapidly compared with ions of other alkali metals

(a) $$BeC{l_2}$$ in aqueous solution exists as $${[Be{\left( {{H_2}O} \right)_4}]^{2 + }}$$ rather than $$B{e^{2 + }}$$ . This is acidic in nature. Explain
(b) $$M{g_3}{N_2}$$ when reacted with water gives $$N{H_3}$$ but HCl is not obtained from $$MgC{l_2}$$ on reaction with water at room temperature.

1351557_1142677_ans_e8b23299686d4a25b77b99a87475031c.jpg

What is the diagonal relationship? Give one example.

A diagonal relationship is said to exist between certain pairs of diagonally adjacent elements in the second and third periods of the periodic table.
Diagonal relationships occur because of the directions in the trends of various properties as you move across or down the periodic table. Many of the chemical properties of an element are related to the size of the atom.
These pairs (lithium (Li) and magnesium (Mg), beryllium (Be) and aluminum (Al), boron (B) and silicon (Si) etc.) exhibit similar properties; for example, boron and silicon are both semiconductors, forming halides that are hydrolyzed in water and have acidic oxides.

Draw a structure of $$BeCl_2$$ in vapour phase.

Structure of $$BeCl_2$$
1326336_1199795_ans_b993fcecc99d4a7080d894aadf4bbb48.png

Among $$KO_2, AlO_2{^-}, BaO_2$$ and $$NO_2^+$$ , unpaired electron is present in:

$$KO_2$$ has unpaired electrons.

Because it contains odd no. of electrons which is $$36$$.

$$\therefore$$ It is clear that it has some unpaired electrons.

1150433_1288395_ans_6b2a875830e4413f8c2ce5ae12bfbc8f.jpg

Rewrite the following by inserting appropriate word/words
(i) Magnesium Nitride reacts with water to liberate Ammonia
(ii) Lead bromide conducts electricity.
(iii) Starch iodide paper turns blue black in the presence of chlorine .
(iv) Hydrogen chloride molecule contains a covalent bond.
(v) Acid salts are formed by replacement of the ionisable hydrogen ions of the acid by a metallic ion or ammonium ion.

(i) Magnesium Nitride reacts with $$\text{'boiling'}$$ water to liberate Ammonia.

$$\text{Reaction:}$$

$$Mg_{3}N_{2}+6H_{2}O\rightarrow 3Mg\left(OH\right)_{2}+2NH_{3}$$

(ii) $$\text{Molten}$$ Lead bromide conducts electricity

(iii) $$\text{Moist}$$ starch iodide paper turns blue-black in the presence of chlorine.

$$\bullet$$ Chlorine turns moist starch iodide paper blue-black because ions on the paper are oxidized to iodine and the starch reacts to it to give a blue-black compound.

(iv) Hydrogen chloride molecule contains a $$\text{polar}$$ covalent bond.

(v) Acid salts are formed by $$\text{partial}$$ replacement of the ionisable hydrogen ions of the $$\text{polybasic}$$ acid by a metallic ion or ammonium ion.

Calcium is an element with the atomic number $$20$$.

(i) Will it be a metal or non-metal?
(ii) What will be its valency?
(iii) What would be the formula of its chloride?
(iv) Will it be smaller or larger than potassium?

The atomic no. of calcium is 20.

Electronic configuration $$= 2, 8, 8, 2$$

The valence electrons in calcium are $$2$$. Thus it is a metal of group $$2$$.

The valency of calcium is $$+2$$ as it has $$2$$ valence electrons.

The chloride of calcium is $$Ca{Cl}_{2}$$ as the valency of chloride ion is $$-1$$ and that of calcium is $$+2$$.

It is smaller than $$K$$ as both elements lie in the third period of the periodic table but $$K$$ lies to the left of $$Ca$$ in the period and we know that atomic size decreases as move right in a period.

Why should a magnesium ribbon be cleaned before it is burnt in air?

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Draw the structure of $${ BeCl }_{ 2 }$$ in vapor phase.

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I heard that magnesium is found in plants. In what form is it found in them ?

Magnesium is the powerhouse behind photosynthesis in plants. Without magnesium, chlorophyll cannot capture sun energy needed for photosynthesis. In short, magnesium is required to give leaves their green color.Magnesium in plants is located in the enzymes, in the heart of the chlorophyll molecule.

Nitrogen, $$N_{2}$$, is the most abundant gas in the Earth's atmosphere and is very unreactive.
Magnesium and lithium both form nitrides with $$N_{2}$$. These compounds both contain the $$N^{3-}$$ ion.
(i) Write an equation for the reaction of magnesium with $$N_{2}$$ to form magnesium nitride.
(ii) Solid lithium nitride, $$Li_{3}N$$, reacts with water according to the following equation.
$$Li_{3}N(s) + 3H_{2}O(I) \rightarrow 3LiOH(aq) + NH_{3}(aq)$$
State one observation you would make during this reaction.

Solution:-

Reaction of magnesium with $${N}_{2}$$-

$$3Mg + {N}_{2} \rightarrow {Mg}_{3}{N}_{2}$$

When solid $${Li}_{3}N$$ reacts with water, solid disappears.

Why are group I elements :
(a) univalent
(b) largely ionic
(c) strong reducing agents
(d) poor complexing agents?
(e) why do they have the lowest first ionization energy values in their periods?

Lithium is the smallest ion in group I. It would, therefore, be expected to have the highest ionic mobility, and hence the solution of its salts would be expected to have a higher conductivity than solutions of caesium salts. Explain why this is not so?

Why are the group I metals soft, low melting and of low density ?

Explain the difference in reactivity of the group I metals with water.

All compounds of alkali metals are easily soluble in water but lithium compounds are more soluble in organic solvents. Explain.

$$Li^{+1}$$ has the smallest size among all the alkali metal ions. Due to its smaller size it has very high polarising power(polarising power=charge/radius). So lithium compounds are covalent in nature(according to fajan's rule). Other alkali metals are ionic compounds. So they are readily soluble in water. But as the lithium compounds are predominantly covalent so they dissolve in organic solvents like alcohol and ether.

Why are $$BeSO_4$$ and $$MgSO_4$$ readily soluble in water while $$SrSO_4$$and $$BaSO_4$$ are insoluble?

Due to the small size of $$Be^{+2} ,Mg^{+2}$$,they possess very high hydration enthalpy which can easily overcome their lattice energy. So $$BeSO_{4},MgSO_{4}$$ are readily soluble in water.On the other hand the hydration enthalpy of $$Sr^{+2},Ba^{+2}$$ is comparatively low which cannot overcome their lattice enthalpy So $$SrSO_{4},BaSO_{4}$$ are insoluble in water.

Describe how you would make lithium hydride. Give equation to show two important properties of lithium hydride. The compound contains the isoelectronic ions $$ Li^{+} $$ and $$ H^- $$ which ion is the larger and why?

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Why and in what ways does lithium resemble magnesium ?

Lithium resembles magnesium in some of its properties. Mention two such properties and give reasons for this resemblance.

Lithium shows diagonal relationship with Mg as the charge to size ratio of Li is comparable to Mg. The periodic properties show either increasing or decreasing trend along the group and vice-versa along the period which makes the diagonally situated elements to have almost similar properties.

$$Period$$ $$Group1$$ $$Group2$$

$$2$$ $$Li$$ $$Be$$

$$3$$ $$Na$$ $$Mg$$

Similar properties of Li and Mg:

a.$$LiCl$$ and $$MgCl_{2}$$ both are soluble in organic solvents like alcohol and pyridine due to high covalent character(Fajan Rule).

b.Their carbonates decompose on heating and release $$CO_{2}$$.

$$Li_{2}CO_{3}\rightarrow Li_{2}O+CO_{2}$$.

$$MgCO_{3}\rightarrow MgO+CO_{2}$$

Identify the final product in each reaction:

1722202_1721566_ans_f8bd1f6c82524ea1a62c2b1d96c20015.png

What is the reason for lithium having a greater tendency to form covalent compound than the other elements in the group ?

Write the balanced chemical equations for the following reaction: Sodium iodate is added to a solution of sodium bisulphite.

When sodium iodate is added to a solution of sodium bisulphite the following reaction occurs:

$$2NaIO_3+5NaHSO_3\rightarrow 3NaHSO_4+2Na_2SO_4+I_2+H_2O$$

Iodine which is commercially important is formed during the reaction.

Give reasons for the following in one or two sentences only: "$$BeCl_2$$ can be easily hydrolyzed".

Beryllium ion is very small in size, and so it has a very high polarizing power (Fajan rules). Also, vacant p-orbitals are available. So beryllium chloride is readily hydrolysed.

Why do beryllium and magnesium not impart colour to the flame in the flame test?

$$Be$$ and $$Mg$$ has very high ionization energy in comparison to other alkaline earth metals due to their small size. The energy of the bunsen flame is not suffieciently high in order to excite the electrons of $$Be$$ and $$Mg$$. Hence $$Be$$ and $$Mg$$ do not show any colour in flame test.

Name the alkaline earth metal which shows resemblance with aluminium.

Beryllium shows resemblance with its diagonally opposite element aluminium.

The $$s-$$ block elements are characterized by their larger atomic sizes, lower ionization enthalpies, invariable + 1 oxidation state and solubilities of their oxosalts. In the light of these features describe the nature of their oxides, halides, and oxosalts.

Due to low ionisation energy and large atomic size, alkali metals form cation readily and so their compounds are ionic.

Oxides: Alkali metals form normal oxides of general formula M₂O. Only Li forms normal oxide Li₂O when heated in air. Other form peroxide and superoxide. Oxides of alkali metals are strongly basic and are soluble in water. The basic character of oxide increases gradually from Li₂O to Cs₂O due to increased ionic character.

Halides: Except lithium halides all other alkali metal halides are ionic. Due to high polarising power of Li⁺ , Lithium halide is covalent in nature. Due to +1 oxidation states alkali metal halides have general formula MX. Low ionisation enthalpy allows formation of ionic halides.

Oxosalts: All alkali metals form solid carbonates of general formula M₂CO₃ . Carbonates are stable except Li₂CO₃ due to high polarising capacity of Li⁺ which is unstable and decomposes. All the alkali metals (except Li) form solid bicarbonates MHCO₃. All alkali metals form nitrates having formula MNO₃. They are colourless, water-soluble, electrovalent compounds.

Arrange the following in increasing order of the property indicated:

Li, Na, K, Rb and Cs (hydrated radii)

$$Cs<Rb<K<Na<Li$$

Answer the following:
Which element of alkaline earth metal has least density?

The densities of alkaline earth metals do not show any regular trend with increasing atomic number.

the density of these metal first decreases from Be to Ca and then increases from Ca to Ba.

So calcium has least density.

The crystalline salts of alkaline earth metals contain more water of crystallization than the corresponding alkali metal salts. Why?

The size of alkaline earth metal ions is lower than the size of alkali metal ions and the charge is higher. The lower the size of the cation and higher the charge, the higher is the hydration energy. So the salts of alkaline earth metals have more water molecules of crystallization than those of alkali metals.

What is the structure of $$BeCl_2$$ molecule in gaseous and solid state?

In the solid state $$BeCl_{2}$$ has a polymeric chain like structure. $$Be$$ atom is surrounded by four $$Cl$$ atoms among which two of them are bonded through covalent bond and other two are through co-ordinate bond. Structure of $$BeCl_{2}$$ is given by structure A.

In gaseous state beryllium chloride exists as dimer($$Be_{2}Cl_{4}$$) which dissociates to the monomer at about 1200K temperature which is linear in structure. Structure of $$BeCl_{2}$$ in gaseous state is given by the structure B.

1883245_1723058_ans_35af74c485724de6b3e6cfeaf9c86585.png

Which elements of group 2 do not give characteristic flame colouration?

$$Be$$ and $$Mg$$

Beryllium and magnesium atoms are smaller in size and their electrons are strongly bound to the nucleus. They need large amounts of energy for excitation of electrons to higher energy levels which is not available in the bunsen flame. So they do not impart colour to the flame.

How does reducing nature of the alkaline earth metals change when we move from Be to Ba?

1686286_1725487_ans_f9ef0dd4cc5745819fde5488a2e944db.jpg

Answer with giving reason:
Which one are strong reducing agents?
Alkali metals or alkaline earth metals.

1735433_1725638_ans_096cbafce75842c69603708353dd4ec7.png

Answer with giving reason:
Which are more electropositive alkali metals or alkaline earth metals?

Alkali metals, are more electropositive due to low ionisation potential.

Alkaline earth metals are less electropositive because of the smaller size and higher ionisation enthalpies of alkaline earth metals as compared to alkali metals.

How do the following properties of the alkaline earth metals change when we move from Be to Ba?
Size of the atoms and ions.

The atomic and ionic radii increases from $$Be$$ to $$Ba$$ due to the effect of extra shells of electrons being added. This outweighs the effect of increased nuclear charge.

How do the following property of the alkaline earth metals change when we move from Be to Ba?
Ionization energy

Ionization energy is simple terms can be described as a measure of the difficulty in removing an electron from an atom or ion or the tendency of an atom or ion to surrender an electron.

Ionization energy decreases along the group. Hence, $$Be> Mg> Ca> Sr> Ba$$

Arrange the following as decreasing order of covalent character
$$LiCl, LiBr$$ and $$LiI$$

Lithium-ion has a small size. Hence it can easily distort the electron cloud of the anion. Hence lithium halides have partial covalent character.

The anion with a larger size can be easily distorted. The increasing order of the ionic size is $$Cl^−<Br^−<I^−$$. Hence among the given halides, lithium chloride is least covalent in nature and lithium iodide is most covalent in nature. Hence the order is $$LiI>LiBr>LiCl$$

Answer the following:
Which out of sodium of potassium has higher melting point?

The melting point of sodium is higher as it has greater metallic bonding than potassium.

Potassium is larger than sodium, so the electrostatic attractions that hold atoms together act at a greater distance, reducing the attractive force, results in its lower melting point.

What happens when following are heated?
Lithium carbonate.

The oxy-salts of lithium are not stable towards heat and decompose on heating forming the stable oxide.

On heating, lithium carbonate decomposes to form lithium oxide and carbon dioxide.

$$Li_2CO_3\rightarrow Li_2O+CO_2$$

Which one is soluble in water, $$LiF$$ or $$KF$$?

$$LiF$$ is more covalent than $$KF$$.

$$LiF$$ has higher lattice energy than $$KF$$.
$$LiF$$ has higher enthalpy of hydration than $$KF$$. $$Li^+$$ ions are not extensively hydrated as $$K^+$$.

Which alkali metal is radioactive in nature?

The most, and only, radioactive alkali metal is francium (Fr).

Answer the following:
Name the alkali metal which shows diagonal relationship?

A Diagonal Relationship is said to exist between certain pairs of diagonally adjacent elements in the second and third periods of the periodic table

$$Lithium$$ which is alkali metal shows diagonal relationship with magnesium.

Answer the following:
Why does table salt get wet in rainy season?

Table salt contains impurities such as $$Na_{2}SO_{4}, CaSO_{4}, MgCl_{2}$$ and $$CaCl_{2}$$. These being hygroscopic absorb moisture from atmosphere. As a result, table salt gets wet.

What happens when?
Sodium is strongly heated in oxygen and the product is treated with $$H_{2}SO_{4}.$$

When heated in an atmosphere of oxygen, alkali metals ignite and form oxides. Lithium forms normal oxide, sodium forms peroxide and potassium, rubidium and caesium forms superoxide.

When Sodium is strongly heated in oxygen, sodium peroxide is formed.

$$2Na+O_2\rightarrow Na_2O_2$$

Peroxide is a strong oxidizing agent. Sodium peroxide when treated with $$H_2SO_4$$, sodium sulphate and hydrogen peroxide are formed.

$$Na_2O_2+H_2SO_4\rightarrow Na_2SO_4+H_2O_2$$

What happens when following are heated?
Lithium nitrate.

The oxy-salts of lithium are not stable towards heat and decompose on heating forming the stable oxide.

On heating, Lithium nitrate decomposes to form lithium oxide, nitrogen dioxide and oxygen.

$$2LiNO_3\rightarrow Li_2O+2NO_2+\dfrac12O_2$$

Match the elements in List-I with their nature in List II

$$(A)\rightarrow 2,3,4$$

Because of higher electronegativity (E.N.=1.5), Be forms covalent hydride
Unlike the oxides formed by the other Group 2 elements (alkaline earth metals), beryllium oxide is amphoteric rather than basic.
Be have small atomic size and high ionization energies when compared to other alkaline earth metals. The energy of flame is not sufficient to excite the electrons of Be to a higher energy level. Hence, Be do not give any color in Bunsen flame.

$$(B)\rightarrow 1,(C)\rightarrow 1$$

$$Fr$$ and $$Ra$$ are radioactive elements, they neither form covalent hydride nor amphoteric oxide.
Radium also imparts crimson color.
Francium also imparts yellow color.

$$(D)\rightarrow 4$$

Mg have small atomic size and high ionization energies when compared to other alkaline earth metals. The energy of flame is not sufficient to excite the electrons of Mg to higher energy level. Hence, Mg does not give any color in Bunsen flame.
Mg form basic oxides
Mg Hydride are ionic in nature

Explain the following with relevant reason.
First ionisation potential of $$Al$$ is lower than that of $$Mg$$.

The electronic configuration of Al and Mg are $$1s^2, 2s^2,2p^6, 3s^2,3p^1$$ and $$1s^2, 2s^2,2p^6, 3s^2$$ respectively. It is easier to remove electron from unpaired p-orbital than the paired s-orbital.

(a) What is the number of valence electrons in the atoms of first element in a period?
(b) What is the usual number of valence electrons in the atoms of the last elements in a period?

(a) The number of valence electrons in the atoms of the first element in a period is 1.

(b) The usual number of valence electrons in the atoms of the last elements in a period is 8.

Which has smaller size $$Na$$ or $$Na^{+}$$?

1691178_1773902_ans_789937ba41944e7d8d653a9f7b5acaee.jpg

Calcium is an element with atomic number $$20$$.
Is it a metal or non-metal?

1693264_1773929_ans_4ebe128cf1d24930be072e4ff2e87e37.jpg

Calcium is an element with atomic number $$20$$.
Is it more or less reactive than $$Mg$$?

1693265_1773931_ans_ab80830e072b47fb868357f2b0726c49.jpg

Which one has the bigger size?
(i) Na or Cl
(ii) Cl or F

1693259_1773924_ans_81be2a71411e4abeb1843bed20b19410.jpg

Calcium is an element with atomic number $$20$$.
What will be its valency?

1693267_1773933_ans_d562273b26c74e89a697e6fa75726b53.jpg

Calcium is an element with atomic number $$20$$.
What will be the formula of its Chloride?

1693269_1773935_ans_9f9bdf9627ed460cbff81a89795ef107.jpg

Calcium is an element with atomic number $$20$$.
Will it be larger than $$K$$ or smaller?

1693270_1773937_ans_48e90fbf493144349dcc395856efddf2.jpg

Which one has the smaller size?
$$K(19)$$ or $$Na(11); B(5)$$ or $$C(6)$$

1693260_1773925_ans_d81fd136e17d4b758fbc92015c6c0c3e.jpg

Which has bigger size; $$Cl$$ or $$Cl^{-}$$?

1691181_1773903_ans_5c7bef1120bd4a4aa1fe542b59456d30.jpg

Which one has larger atomic size $$Cl$$ or $$Br$$ ? Why ?

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Why is the size of sodium greater than magnesium ?

Since atomic number of magnesium is more than sodium but the numbers of shells are same, the nuclear pull is more in case of Mg atom. Hence its size is $$\textbf{smaller}$$ than sodium.

Explain the following :
Size of an atom progressively becomes smaller when we move from sodium ($$Na$$) to chlorine ($$Cl$$) in the third period of the periodic table.

In a period , the size of an atom decreases from left to right . This is because the nuclear charge , i.e., the atomic number increases from left to right in the same period, thereby bringing the outermost shell closer to the nucleus . Therefore , considering the third period given above , it has been found that sodium is the largest size , while chlorine is the smallest.

Match the elements given in Column I with the properties mentioned in Column II.

$$(\mathrm{i}) \rightarrow(\mathrm{c}) ;(\mathrm{ii}) \rightarrow(\mathrm{b}) ;(\mathrm{iii}) \rightarrow(\mathrm{d}) ;(\mathrm{iv}) \rightarrow(\mathrm{a}),(\mathrm{e}) $$

$$\mathrm{Column- I}$$	$$\ \ \ \ \ \ \ \ \ \ \ \mathrm{Column-II}$$
Li	Due to very high hydration enthalpy, $$ E^{0} $$ is most negative.
Na	Na gives NaOH (strong base). One mole of it replaces 1 mol $$H^+$$from acid therefore it is the strongest monoacidic base.
Ca	Hydration energy is very low therefore, calcium oxalate is insoluble.
Ba	Hydration energy is low as the size $$ \mathrm{Ba}^{2+} $$ is large therefore barium sulphate is insoluble. $$ 6 \mathrm{s}^{2} $$ is valence shell electronic configuration.

Why are alkali metals kept in kerosene oil?

Alkali metals like sodium and potassium are kept in kerosene as they react with moisture and air.

An element has $$ 2 $$ electrons in its N shell.
State the name assigned to this group ?

The element is Calcium.
It's atomic no. is 20.
It's position in periodic table is group $$II\;B$$ and period 4.

Present a comparative account of the alkali and alkaline earth metals with respect to the following characteristics:
(i) Tendency to form ionic/covalent compounds

(i) Alkaline earth metals give ionic compounds but these compounds are less ionic than alkali metals because of more effective nuclear charge and small size.

Also all alkali except Li form ionic compounds.

And all alkaline earth metals except Be form ionic compounds.

Try to find it
...... glass dissolves in water.

Water glass, also called sodium silicate or soluble glass, a compound containing sodium oxide $$(Na_{2}O)$$ and silica (silicon dioxide,$$SiO_{2}$$) that forms a glassy solid with the very useful property of being soluble in water.

Hence , Alkali silicate glass dissolves in water.

Hence, correct answer is Alkali silicate.

The alkali metals have no tendency to show variable oxidation states. Give reason.

Alkali metals show oxidation state of +1. With the loss of valence electron it attains the stable configuration of nearest inert gas. Its second ionization potential is high. Hence an alkali metal does not show variable oxidation states.

Why are group 1 elements called alkali metals ?

It is because their hydroxides are soluble bases called alkalies. Secondly their ashes are alkaline in nature.

Why do alkali metals have low ionisation energy ?

It is due to largest atomic size, they can lose electrons easily.

Variation of first ionization enthalpies with $$Z=1$$ to $$60$$.
Study the figure given above and answer the following:
(a) Compounds of Xe are known but other noble gases do not form compounds
(b) Giving reason arrange alkali metals in increasing order of first ionization enthalpies
(c) Estimate the first ionization enthalpy values of $$Mg$$ and $$Al$$.

(a) Ionisation energy of Xe is minimum, hence electron can be taken out from it stable noble gas configuration allowing it to make some compounds,

(b)

Li>Na>K>Rb>CsLi>Na>K>Rb>Cs.

What are alkalies?

Bases which are soluble in water are called alkalies.

Name :
The element of period $$ 3 $$ valency $$ 4 $$.

Silicon

LiCI and MgCk dissolve in alcohol. How do you explain this?

Both LiCI and $$MgCl_2$$ are covalent compounds and dissolve in alcohol. This is due to high polarizing power of $$Li^+$$ and $$Mg^{2+}$$ ions.

This question refers to the elements of the periodic table with atomic number from $$ 3 $$ to $$ 18 $$. Some of the elements are shown by letters , but the letters are not the usual symbols of the elements.

$$3$$ $$4$$ $$5$$ $$6$$ $$7$$ $$8$$ $$9$$ $$10$$
A B C D E F G H
$$11$$ $$12$$ $$13$$ $$14$$ $$15$$ $$16$$ $$17$$ $$18$$
I J K L M N O P

Which of these is an alkali metal ?

Atomic number $$3$$ and $$11$$ are alkali metals - $$A$$ and $$I$$

Arrange the following in order of increasing radii :
$$ Mg^{2+} , Mg , Mg^{+} $$

$$ Mg^{2+} < Mg^+ < Mg $$

For isoelectronic species, cations with higher charge are smaller in size

Why does ionisation energy of alkali metals decrease with the increase in atomic number ?

Atomic size increases with increase in atomic number, therefore, nuclear force of attraction between valence electrons and nucleus decreases, hence ionisation energy decreases down the group.

Why are alkali metals used in photoelectric cells ?

They have low ionisation energy and can lose electrons when light falls on them, that is why they are used in photoelectric cells.

Why do alkali metals have low melting and boiling points ?

It is due to weak metallic bonds which is due to bigger atomic size that is why they how low melting and boiling points.

Why is second ionisation energy of alkali metals higher than alkaline earth metals ?

Alkali metals acquire, noble gas configuration after losing 1 electron, therefore their second ionization energy is higher than alkaline earth metals

Why is potassium more reactive than sodium ?

K has lower ionisation energy than sodium due to bigger atomic size, therefore, it is more reactive.

Why do alkali metals not occur in free state ?

They are highly reactive, therefore, they occur in combined state and do not occur in free state.

Why do alkali metals give characteristic flame colouration?

They have low ionization energy and absorb energy from visible region of spectrum and radiate complementary colour.

Write electronic configuration of Na (11) and K (19).

$$Na(11):1s^2 2s^2 2p^6 3s^1\, k(19): 1s^2 2s^2 2p^2 3s^13p^64s^1$$

Complete the reaction : $$Lil + KF \rightarrow$$

$$Lil + KF \rightarrow LiF+Kl$$;larger cation stabilizes larger anion and smaller cation stabilizes smaller anion.

Why group 2 elements (Mg and Ca) are harder and denser than group 1 elements ?

They have strong metallic bonds due to smaller size and have more number of valence electrons.

Discuss the diagonal relationship of $$Be$$ and $$Al$$ with regard to
$$\cdot$$ the action of alkali and
$$\cdot$$ the structure of the chlorides.

$$Be$$ and $$Al$$ resemble with each other due to same charge over radius ration.

$$\cdot$$ Both $$B$$ and $$Al$$ amphoteric oxides

$$\cdot$$ $$Be$$ and $$Al$$ form covalent compounds

$$\cdot$$ $$BeCl_2$$ exists as polymer whereas $$AlCl_3$$ exists as dimmer

$$\cdot$$ Both $$Be$$ and $$Al$$ react with $$NaOH$$ to form similar compounds.

Why does Be resemble Al?

Be resembles Al because charge over radius ratio is similar, i.e., they have similar polarizing power.

Name the metal which floats on water without apparent reaction.

Berylium.

Why does lithium show anomalous behaviour ?

Due to its small size and high charge/size ratio.

Give reason for diagonal relationship of lithium with magnesium.

Both Lithium and magnesium have small size and high charge density. The electronegativities of Li is 1.0 and Mg is 1.2. They are low and almost same. Their ionic radii are similar. Hence they show similarities which is known as diagonal relationship between first element of a group with the second element in the next higher group.

Why is oxidation state of Na and K always + 1?

It is due to their high second ionization enthalpy and stability of their ions $$[Na^+ K^+]$$

Name the elements (alkali metals) which form superoxide when heated in excess of air.

Potassium, rubidium and caesium

Compare four properties of alkali metals and alkaline earth metals.

Alkali Metals	Alkaline earth metals
The show + 1 oxidation state.	They show + 2 oxidation state
They are soft metals	They are harder than alkali metals.
They do not form complexes except Li.	They can form complex compounds
Their carbonates are soluble in water except $$Li_2CO_3$$	Their carbonates are insoluble water.

Give two important ores each of Na and K.

Rock salt $$(NaCI), Na_2CO_3, NaHCO_3, 2H_2O$$ (trona) are important ores of Na. Sylvine $$(kCl); kCl.mgcl_2.6H_2O$$ (carnallite) are of k.

Write balanced equations for the following reactions and name the main product formed in each case,
$$\cdot NaBH_4 + I_2\rightarrow$$
$$\cdot B_2H_6 + NaH\rightarrow$$
$$\cdot BF_3 + LiH \overset{450K}{\rightarrow}$$
$$\cdot SiCl_4 + H_2O\rightarrow$$

$$\cdot 2NaBH_4 + I_2\rightarrow 2NaI + + H_2 + B_2H_6$$ (Diborane)

$$\cdot B_2H_6 + 2NaH\rightarrow 2NaBH_4$$ (sodium borohydride)

$$\cdot 2BF_3 + 6LiH\xrightarrow{450K} 6LiF + B_2H_6$$ (Diborane)

$$\cdot SiCl_4 + 2H_2O\rightarrow 4HCl + Si(OH)_4$$ (Silicic acid)

Discuss the diagonal relationship of Be and Al with regard to
action of alkali and
the structure of their chloride.

Be and Al both react with NaOH to form sodium beryllate and sodium meta aluminate respetively. Be dissolves in excess of NaOH to form $$[Be(OH)4]^2$$ where as Al forms $$[ Al (OH)6 ]^{3-}$$ in excess of NaOH.

$$2H_2O + Be + 2NaOH\rightarrow Na_2 [Be (OH)4 ] (saliun beryllali) + H_2$$

$$2A1 + 6NaOH + 6H_2O —> 2Na_3 [ Al (OH)6] (Sodiam meta ilumivali) + 3H2 $$

1771030_1827725_ans_c93f8e04ee2741bb89a27996366679ff.png

Why is it that the s-block elements never occur in free state/nature? What are their usual modes of occurrence and how are they generally prepared?

The elements belonging to s-block in periodic table (i.e. alkali and alkaline earth metals) are highly reactive because of their low ionization energy. They are highly electropositive forming positive ions. So they are never found in free state. They are widely distributed in nature in the combined state. They occur in earth's crust in the form of oxides, chlorides, silicates and carbonates. Generally group I metals are prepared by the electrolysis of fused solution. As for example:
(i)$$ NaCI\rightarrow Na^+ + Cl^-$$
At anode $$Cl\rightarrow Cl+e^{-}$$
$$Cl+Cl\rightarrow Cl_2$$
AT cathode: $$Na+e^-\rightarrow Na$$
ii) $$KOH \rightleftharpoons K^++OH^-$$
At anode: $$4OH^-\rightarrow 4OH^-+4e^-$$
$$4OH\rightarrow 2H_2O+O_2$$
or $$ 4OH^-\rightarrow 2H_2O+O_2+4e^-$$
At cathode: $$K^++e^-\rightarrow k$$
These metals are highly reactive and therefore cannot be extracted by the usual methods, because they are strong reducing agents.

What are alkali metals? Describe their general properties.

1st group elements of periodic table i.e., lithium, sodium, potassium, rubidium and caesium are called alkali metals.
General properties:
• Alkali metals have general electronic configuration ns1 E
• Alkali metals exhibit on oxidation state of+1.
• Atomic radius increases down the group from lithium to caesium.
• The metallic property of alkali metals increases from lithium to caesium.
• Alkali metals have low ionization potential.
• Due to low ionization power they are highly electropositive.
• Alkali metals are light metals.

Which out of Li, Na, K, Be, Mg, Ca has lowest ionization enthalpy and why ?

K has lowest ionisation energy due to larger atomic size among these elements. The force of attraction between valence electron and nucleus is less, therefore, it can lose electron easily.

Name an alkali metal carbonate which is thermally unstable and why ? Give its decomposition reaction.

$$Li_2CO_3$$ is thermally unstable because it is covalent. It decomposes to form $$Li_2O$$ and $$CO_2; Li_2CO_3\rightarrow Li_2O + CO_2$$

The ionic compounds of alkali metals are colourless, why?

Alkali metals form unipositive ions which have stable configuration of the nearest inert gas. Alkali metal salts are diamagnetic and colorless because they do not have impaired electrons.

What makes lithium show properties uncommon to the rest of alkali metals ? Write two points of similarly in properties between lithium and magnesium.

Solubility of sulphates goes on decreasing down the group because lattice energy dominates over hydration energy. Lithium has smallest atomic size and highest ionization energy, highest polarizing power that is why it shows uncommon properties to the rest of alkali metals.
• Both Lithium and Magnesium react with N2 to form nitrides.
• Li and Mg react with 02 to form monoxides.

Which metal is present in chlrophyll ? How does this metal react with $$N_2$$ ?

Mg is present in chlorophyll. N2 reacts with Mg to form magnesium nitride. $$3Mg + N_2\rightarrow Mg,N_2$$ (magnesium nitride)

The $$E^0$$ for $$C1^-/Cl_2$$ is 1.36, for $$I^-/I^2$$ is +0.53, for $$Ag^+/Ag$$ is + 0.79, $$Na^+$$ is -2.71 and for $$Li^+ / Li$$ is -3.04 V Arrange the following species in decreasing order of reducing strength.$$ I^-, Ag, Cl^- Li, Na$$

The more negative or less positive is the electrode potential, more is the reducing strength of the species. Since the electrode potentials inceases in the order : $$Li(-3.04V) < Na(-2.7V) < I^-(0.53 V) < Ag(+0.79V) < Cl^- (+1.36V)$$, therefore, the reducing strength decreases in the order $$ Li > Na > I^- > Ag > Cl^-$$

Lithium does not show similarity with other elements of the group. Explain the reasons.

Lithium does not shows similarity with other elements of the group due to following reason-

1. Exceptionally small size of its atom and ion.

2.high polarizing power(i.e., charge/ radius ratio),

3. high ionization energy and least electropositive character.

4. absence of d-orbitals.

In a period, melting points of alkali metals are lower than alkaline eath metals, why?

In a period, melting points of alkali metals are lower than earth metals because alkali metals have weak metallic bond between them due to presence of only one valence electron.

What is diagonal relationship? How beryllium shows similarity with Aluminium?

Diagonal relationship- A diagonal relation ship is exist between certain pairs of diagonally adjacent elements in the second and third periods of the periodic table. e.g., $$Li $$ and $$Mg $$, $$ Be $$ and $$Al,B $$ and $$Si $$ etc.

Beryllium shows similarity with aluminium because these elements exhibit diagonal relationship, The similarities are-

1. Beryllium hydroxide and aluminium hydroxide reacts with excess alkali to form respective ions.

2. Both these elements have the capacity to withstand the acid attack due to presence of an oxide film on the surface of the metal,

Write balanced equation for relation between

$$Be_2 C $$ and water

Reaction between $$Be_2C $$ and water

$$Be_2C+4H_2O \rightarrow 2Be(OH)_2+CH_4 $$

Why potassium and calcium are used in photoelectric all in place of Lithium?

Potassium and calcium are used in photoelectric cell in place of lithium due to their low-ionization energies.

The are used as electrodes in photoelectric call.

Alkali metals are strong electropositive in nature, Why?

Alkali metals are strong electropositive in nature because they have low ionization energies and their atoms readily lose the valence electron.

Why lithium compounds are covalent in nature?

Lithium compounds are covalent in nature because lithium is the smallest atom in group $$ 1 $$ so the attraction between the outer electrons and the nucleus is greater. So, it is very hard for it to lose electrons to another element to form a compound by an ionic bond.

Sodium is kept in Kerosene. Why?

$$Na$$ reacts with air (oxygen) and water, as it is reactive metal.

Compare the alkali metals and alkaline earth metals with respect to
Ionisation enthalpy
Atomic and ionic radius

1. Ionisation enthalpy: The first ionisation enthalpies of alkaline earth metals are higher than those of alkali metals due to high nuclear charge. However second ionisation enthalpies of alkaline earth metals are lower then those of corresponding alkali metals.

2.Atomic and ionic radius:

Atomic and ionic radii of alkaline earth metals are lesser than those of alkali metals due to increases nuclear charge.

Lithium has the highest ionization enthalpy in group I elements, yet it is the strongest reducing agent. why?

Lithium has highest ionization enathalpy in group I elements , yet it is the strongest reducing agent because lithium has the highest oxidation potential.

Which out of sodium or potassium has higher melting point ?

On going from $$ Na $$ to $$ K $$ , the size of the atom increases and hence the metallic bonding weakens. In other words sodium has high melting point then potassium because of stronger metallic bonding.

What is diagonal relationship due to ?

Diagonal relationship due to similar size of atoms or ions, similar electronegativity or similar polarising power.

What makes lithium to show properties uncommon to the rest of the alkali metals?

The unusual properties of lithium as compared to other alkali metals is due to

(i) the exceptionally small size of its atom and ion and

(ii) high polarising power (charge/ size ratio).

Name the alkaline earth metal which forms covalent compounds.

$$ Be $$ forms covalent compounds.

State any one reason for alkaline earth metals having a greater tendency to form complexes than alkali metals.

Alkaline earth metals having a greater tendency to form complexes than alkali metals because of smaller size and higher charge on alkaline earth metal contains as compared to the corresponding alkali metal cations, alkaline earth metal cations have a greater tendency to form complexes.

Name the alkali metal which shows diagonal relationship with magnesium.

$$ Li $$ shows diagonal relationship with magnesium.

Name the chief factor responsible for the anomalous of lithium.

The chief factor responsible for the anomalous of lithium is small size, high electronegativity and high ionization enthalpy.

$$ 6 \cdot 70 \mathrm{g} $$ of an alkali metal oxalate was dissolved per litre of the solution. $$ 10 \mathrm{cm}^{3} $$ of this solution required $$ 20 \mathrm{cm}^{3} $$ of $$ 0.01 \mathrm{M} $$ potassium permanganate solution in acidic medium. What is the atomic weight of the alkali metal.

The balanced chemical equation for the redox reaction is
$$\begin{array}{c}2 \mathrm{KMnO}_{4}+5(\mathrm{COOM})_{2}+8 \mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \\\mathrm{K}_{2} \mathrm{SO}_{4}+2 \mathrm{MnSO}_{4}+5 \mathrm{M}_{2} \mathrm{SO}_{4}+10 \mathrm{CO}_{2}+8 \mathrm{H}_{2} \mathrm{O}\end{array}$$
where $$ \mathrm{M} $$ is the alkali metal
Let $$ M_{1} $$ be the molarity of the alkali metal oxalate solution. Applying molarity equation, we have,
$$\dfrac{M_{1} \times 10}{5}=\dfrac{20 \times 0 \cdot 01}{2} \text { or } M_{1}=0 \cdot 05 M$$
Let $$ A $$ be the atomic weight of the alkali metal.
$$ \therefore \quad $$ Mol. wt. of $$ (\mathrm{COOM})_{2}=2 \mathrm{A}+88 $$
Thus, amount of metal oxalate present per litre of the solution $$ =(2 A+88) \times 0.05 g $$
But the amount of alkali metal oxalate solution
$$=6 \cdot 7 \mathrm{g} \mathrm{L}^{-1} \quad(\text { given })$$
$$\therefore \quad(2 \mathrm{A}+88) \times 0.05=6 \cdot 7 \quad \text { or } \mathrm{A}=23$$

Which alkaline earth metal is radioactive?

$$ Ra $$ is radioactive alkaline earth metal.

Why does beryllium show similarities with aluminium ?

Due to same electronegativity $$ (1.5) $$ and very similar polarizing power $$(Be^{2+} =0.064 $$ and $$ Al^{3+}=0.060) $$ of their ions.

Why alkaline earth metals have a greater tendency to form complexes than the alkali metals?

Alkaline earth metals have a greater tendency to form complexes than the alkali metals due to higher nuclear charge.

Fill in the blanks :
lithium resembles more with _____ than with sodium.

Lithium resembles more with $$ magnesium $$ than with sodium.

Write three general characteristics of the element of s-block of the periodic table which distinguish them from the elements of the other blocks.

$$\text { Physical Propertics of alkali metelis : - } \\$$

$$\text { (i) All alkali metals are silvery white, soft and light metal, } \\$$

$$\text {because of the large size, these elements have low density }$$

$$\text { 2) The melting point, boiling point of alkali metals are low } \\$$

$$\text { because of weak metallic bonding due to the presence } \\$$

$$\text { of only a single valence electron. }$$

$$\text { 3.) } \text {In whole periodic table Alkali metals have lowest } \\$$

$$\text { ionisation enthalpy and Hydration enthalpy and have } \\$$

$$\text { highest oxidation potential. } \\$$

$$\text {They are good conducturs of heat and electricity. } \\$$

$$\text {They are soluble in liquid ammunia. }$$

Fill in the blanks :
The _______ of Be is highest among the alkali metals.

The $$ ionization \ energy \ or \ electronegativity $$ of Be is highest among the alkali metals.

Fill in the blanks :
$$ Ca^{2+} $$ has a smaller ionic radius than $$ K^+ $$ because it has _______.

$$ Ca^{2+} $$ has a smaller ionic radius than $$ K^+ $$ because it has $$ Higher \ effective \ nuclear \ charge $$

Match compounds given in List 1 with their use in List 2

Liquid sodium metal is used as a coolant (heat-transfer medium) in a nuclear reactor.

Potassium is used in the preparation of potassium hydroxide which is used in the manufacture of soft soap.

Potassium nitrate is used in ceramics, colour TV tubes, fluorescent light tubes and explosive stearate.

Potassium superoxide is used in breathing apparatus, submarine and space capsules.

$$\displaystyle KO_2 $$ reacts directly with $$CO$$ and $$\displaystyle CO_2 $$ producing $$\displaystyle O_2$$ as follows:

$$\displaystyle 2KO_2 + CO \rightarrow K_2CO_3 + O_2$$

$$4KO_2 + 2CO_2 \rightarrow 2K_2CO_3 + 3 O_2 $$

$$4KO_2 + 4CO_2 +2H_2O \rightarrow 4KHCO_3 +3O_2 $$

The single-bonded metallic radius of sodium is $$157$$ pm. Assume that the increment between radii of different magnitudes is $$60$$ pm. The covalent radius of Na in pm is $$(90+x)$$. Find $$x$$.

The valence electrons are mobile and weakly attracted. However, the metallic forces are weaker than covalent forces. Hence, the metallic radius is larger than the covalent radius. The single-bonded metallic radius of sodium is 157 pm.
The increment between radii of different magnitudes is 60 pm.

The covalent radius of Na in pm is $$157 \: pm -60 \: pm = 97 \: pm$$.

$$\therefore 90+x= 97 pm \Rightarrow x=7 pm$$

$$Ca^{2+}$$ can be determined by precipitating it as $$CaC_2O_4$$ gravimetrically. The percentage of $$Ca^{2+}$$ in a sample, if 0.5 g of $$Ca^{2+}$$ salt gave 1.28g of $$CaC_2O_4 $$ is
Given $$(Ca = 40, Ca = 12, O = 16)$$

The molar mass of $$CaC_2O_4$$ is $$40+2(12)+4(16)=128 \: g/mol$$

Thus, 128 g $$CaC_2O_4$$ corresponds to 40 g $$Ca^{2+}$$.

Hence, 1.28 g $$CaC_2O_4$$ will correspond to 0.4 g $$Ca^{2+}$$.

Hence, the percentage of $$Ca^{2+}$$ in the sample $$= \cfrac {0.4 \: g}{0.5 \: g} \times 100 = 80$$%.

The single-bonded metallic radius of sodium is $$157$$ pm. Assume that the increment between radii of different magnitudes is $$60$$ pm. The ionic radius $$Na^{+}$$ in pm is $$(90 + x)$$. Find $$x$$.

Metallic radius is larger than ionic radius. The single-bonded metallic radius of sodium is 157 pm. The increment between radii of different magnitudes is 60 pm.Hence, the ionic radius of $$Na$$ in pm is $$157 \: ppm -60 \: ppm = 97 \: ppm$$.

$$\therefore 90+x= 97 pm \Rightarrow x=7 pm$$

"While comparison of $$Li^{+}$$ and $$Na^{+}$$ salts in terms of property of complex formation we found that $$[Li(NH_3)_4]$$ exists and $$Na$$ does not form any complex."
Answer whether the above statement is true or false.
If true enter 1, else 0

The statement is true.

While comparison of $$Li^{+}$$ and $$Na^{+}$$ salts in terms of property of complex formation, we found that $$[Li(NH_3)_4]$$ exists and $$Na$$ does not form any complex.

Because of their low positive charge (+1) and relatively large ionic radii, alkali metal cations have only a weak tendency to react with simple Lewis bases to form metal complexes. Complex formation is most significant for the smallest cation ($$Li^+$$) and decreases with increasing radius. Complex formation is primarily due to the electrostatic interaction of the metal cation with polar molecules.

Hence, Na doesnot form any such complex.

Entries in List 1 are to be matched with entries of List-Each entry of List-1 may have matching with one or more than one entries in List-2.

(A) Magnesium hydroxide $$\displaystyle Mg(OH)_2 $$ is used as a constituent of sorrel cement.
(B) Barium sulphate $$\displaystyle BaSO_4 $$ is used as a constituent of lithopone.
(C) Magnesium sulphate $$\displaystyle MgSO_4 $$ is used as purgative in medicine.
(D) Calcium cyanide $$\displaystyle Ca(CN)_2 $$ is used as a fertilizer.

Lithium on heating in air forms mainly $$Li_2O$$ (oxide) and not peroxide $$(Li_2O_2)$$. If true enter 1 else 0.

Lithium on heating in air forms mainly $$Li_2O$$ (oxide) and not peroxide $$(Li_2O_2)$$.
$$Li^{+}$$ being smaller in size cannot stabilize larger anion as $$O^{2-}_{2}$$ (peroxide). Thus, $$Li_2O_2$$ is not formed.

Match List I (Compounds) with List II (Associated Uses).

(A) $$\displaystyle KO_2 $$ (Potassium superoxide) is used in space capsules, submarines and breathing masks as it removes $$\displaystyle CO_2 $$ and produces $$\displaystyle O_2 $$
$$\displaystyle 4KO_2 + 2CO_2 \rightarrow 2 K_2CO_3 + 3O_2 $$
(B) Sodium hydrogen carbonate $$\displaystyle NaHCO_3 $$ is used in the preparation of baking powder.
(C) Lithium chloride $$\displaystyle LiCl$$ is used for humidity control.
(D) Cesium metal (Cs) is used form photovoltaic cell.

Lithium being heated in air mainly forms the monoxide and not the peroxide. If true enter 1 else 0.

Match the cations from List I with their properties in List II.

$$Li^+_{(aq)}$$:
Lithium readily reacts vigorously with halogens to form ionic halides.
$$2Li+Cl_2 \rightarrow 2LiCl$$
Lithium ion has highest hydrated size among the ions and highest hydration energy among the cations.
It has lowest ionic mobility among the ions.

$$Na^+_{(aq)}$$:
Sodium readily react vigorously with halogens to from ionic halides.
$$2Na+Cl_2 \rightarrow 2NaCl$$

$$K^+_{(aq)}$$:
Potassium readily reacts vigorously with halogens to form ionic halides.
$$2K+Cl_2 \rightarrow 2KCl$$

$$Rb^+_{(aq)}$$:
Rubidium readily reacts vigorously with halogens to form ionic halides.
$$2Rb+Cl_2 \rightarrow 2RbCl$$
It has highest ionic mobility among the ions.

Compare the solubility and thermal stability of the following compounds of the alkali metals with those of the alkaline earth metals. (a) Nitrates, (b) Carbonates, (c) Sulphates.

(i) Solubility
Nitrates, carbonates and sulphates of alkali metals are water soluble. On moving down the group, the solubility increases. This is because their lattice energies decreases more rapidly than their hydration energies.
Alkaline earth metal nitrates are water soluble. On moving down the group, their solubility decreases. This is because their hydration energies decreases more rapidly than their lattice energies.
Alkaline earth metal carbonates and sulphates have lower solubility than alkali metal carbonates and sulphates. The solubility of alkaline metal carbonates and sulphates decreases with decrease in hydration energy as we move down the group.
(ii) Thermal stability
Alkali and alkaline earth metal nitrates decompose on heating. On heating alkali metal (Na, K, Rb and Cs) decompose to form metal nitrites and oxygen.
$$\displaystyle 2MNO_3 \xrightarrow {heat} 2MnO_2+O_2 $$
Alkaline earth metal nitrates decompose on heating to give metal oxide, nitrogen dioxide and oxygen.
$$\displaystyle 2M(NO_3)_2 \xrightarrow {heat} 2MO + 4NO_2+O_2 (M=Be, Mg, Ca, Sr, Ba)$$
Lithium nitrate (like magnesium nitrate) decomposes to form metal oxide, nitrgen dioxide and oxygen.
$$\displaystyle 4LiNO_3 \xrightarrow {Heat} 2Li_2O +4NO_2+O_2 $$
This is because small sized Li+ ion cannot stabilize nitrate ion.
Alkaline earth metal carbonates have less stability towards heat and decompose to carbon dioxide.
$$\displaystyle MCO_3 \rightarrow MO + CO_2 $$
On moving down the group, the stability of alkaline earth metal carbonates increases. Because of diagonal relationship, lithium carbonate decomposes similar to magnesium carbonate.
$$\displaystyle Li_2CO_3 \xrightarrow {heat} Li_2O + CO_2 $$
Other alkali metal carbonates being stable to heat do not decompose.
On heating, alkaline earth metal sulphates decompose to form $$\displaystyle SO_3 $$
$$\displaystyle MSO_4 \xrightarrow {heat} MO+SO_3 $$
On moving down the group, the electropositive characteer and the thermal stability of alkaline earth metal sulphates increases.
Except $$\displaystyle Li_2SO_4 $$, the alkali metal sulphates are stable and do not decompose easily.
$$\displaystyle Li_2SO_4 $$ decomposes like $$\displaystyle MgSO_4 $$ to give $$\displaystyle SO_3 $$
$$\displaystyle Li_2SO_4 \xrightarrow {heat} Li_2O + SO_3 $$
$$\displaystyle MgSO_4 \xrightarrow {heat} MgO + SO_3 $$

In what ways lithium shows similarities to magnesium in its chemical behaviour?

Chemical similarities between $$Li$$ and $$Mg$$:
(1) Their reaction with cold water is slow.
(2) The solubility of the oxides of $$Li$$ and $$Mg$$ in water is low. At high temperature, the hydroxides decompose.
$$\displaystyle 2LiOH \xrightarrow {Heat} Li_2O + H_2O $$
$$\displaystyle Mg(OH)_2 \xrightarrow {Heat} MgO + H_2O $$.
(3) They form nitrides by reaction with nitrogen.
$$\displaystyle 6Li + N_2 \xrightarrow {heat} 2Li_3N $$
$$\displaystyle 3Mg + N_2 \xrightarrow {heat} Mg_3N_2 $$
(4) They do not form peroxides or superoxies.
(5) They form covalent carbonates which decompose on heating.
$$\displaystyle Li_2CO_3 \xrightarrow {heat} Li_2O + CO_2 $$
$$\displaystyle MgCO_3 \xrightarrow {heat} MgO + CO_2 $$
(6) They do not form solid bicarbonates.
(7) Their covalent chlorides are soluble in ethanol.
(8) Their chlorides are deliquescent and crystallize from aqueous solution as hydrates such as $$\displaystyle LiCl_2.2H_2O $$ and $$\displaystyle MgCl_2.8H_2O$$

Explain the significance of sodium, potassium, magnesium and calcium in biological fluids.

The cations of Na and K are present in red blood cells. The concentration gradient (the ratio $$\displaystyle K^+:Na^+ $$) in mammals (humans, rabbits, rats and horses) is $$7:1$$. This ratio in cats and dogs is $$1: 15$$. Work has to be done to establish this concentration gradient. This is done by various mechanisms involving sodium pump and potassium pump. These gradients control the development and functioning of nerve cells.

Chlorophyll contains $$\displaystyle Mg^{2+} $$ ions. Chlorophyll absorbs sunlight and carries the process of photosynthesis.

$$\displaystyle Ca^{+2} $$ ions are present as phosphates in bones of humans and animals. They play an important role in muscle contraction. Their deficiency causes malnutrition in children.

Both $$\displaystyle Ca^{2+} $$ and $$\displaystyle Mg^{2+} $$ ions catalyze the formation of pyrophosphate linkages which control the various biological systems.

Why is $$LiF$$ almost insoluble in water whereas $$LiCl$$ is soluble not only in water but also in acetone?

(1) For a substance to dissolve in water, its hydration energy must be greater than its lattice energy, (2) Due to the small size of $$Li^+$$ ion and $$F^-$$ ions, lattice energy of $$LiF$$ is very high. $$LiF$$ is covalent in nature, Therefore, $$LiF$$ is insoluble in water. (3) Due to the larger size of $$Cl^-$$ ion, the lattice energy of $$LiCl$$ is less than its hydration energy. Hence, $$LiCl$$ is soluble in water and in acetone.

It may be noted that lithium has most negative $$E^{\Theta}$$ value (table 9.1). But its reaction with water is less vigorous than that of sodium which has the least negative $$E^{\Theta}$$ value among the alkali metals. This behaviour of lithium is attributed to its small size and very high hydration energy. Other metals of the group react explosively with water.

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What is diagonal relationship ? Give two examples to illustrate the concept ?

A diagonal relationship in $$S$$-block elements exists between adjacent elements which are located in the second and third period of the periodic table.

For example, Lithium of group $$1A$$ and second period shows similarities with the properties of magnesium which are located in the 2nd group and 3rd period. Similarly, properties of beryllium which are located in 2nd group and 2nd period show a likeness with properties of aluminum which is located in the third period and third group. The two elements which show similarities in their properties can be called a diagonal pair or diagonal neighbors.

The properties of these elements vary significantly when compared to the other elements of the sub-group they belong to. The diagonal neighbors show a lot of similarities. Such a relationship is exhibited as you move left to right and down the group; the periodic table has opposing factors.

For example, the electronegativity of the elements increases as we go across the period and decreases as we go down the group. Therefore when it is moved diagonally the opposite tendencies cancel out and the value of electronegativity almost remains same.

Write chemical formula of washing soda. How is it obtained from baking soda? Name the one industrial use of washing soda other than washing clothes.

The chemical formula of washing soda is $$Na_2CO_3.10H_2O$$

Washing soda can be obtained by heating baking soda.

On heating, baking soda gives sodium carbonate, carbon dioxide and water.

Washing soda is used in glass, soap and paper industries.

Present a comparative account of the alkali and alkaline earth metals with respect to the following characteristics.
a. Tendency to form ionic/covalent compounds
b. Nature of oxides and their solubility in water
c. Formation of oxosalts
d. Thermal stability of oxosalts

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How do you account for the strong reducing power of lithium in aqueous solution?

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Which of the following methods would you use to extinguish a fire of lithium, sodium or potassium metals? Explain why some of these are unsuitable, and give the reactions involved.
(a) water
(b) nitrogen
(c) carbon dioxide
(d) asbestos blanket

The four general methods of extracting metals are thermal, decomposition, displacement of one element by another, chemical reduction and electrolytic reduction. how are the group I metals obtained and why are the other methods unsuitable?

The stability of peroxide and superoxide of alkali metals increase as we go down the group. Explain giving reason.

As we go down the group the size of alkali metal ion increases and the stability of peroxides and super oxides also increases. This is due to the stabilization of larger anions by larger cations.
As we move from Li⁺ to Cs⁺the size of the cations increases.

Li⁺ is the smallest cation with strong positive field around it. Hence it combines with small anion called oxide ion (O^-2) with strong negative field and form Lithium oxide.
Na⁺ ion is bigger than Li⁺ion with less positive field around it combines with peroxide ion (O₂^-2) with less negative field and form sodium peroxide.

K⁺, Rb⁺and Cs⁺ ions are bigger in size with less positive field around them. Hence they can stabilize the bigger superoxide ion (O₂^-) with less negative field and form super oxides.

Element A burns in nitrogen to give an ionic compound B. Compound B reacts with water to give C and D. A solution of C becomes 'milky' on bubbling carbon dioxide. Identify A, B, C and D.

The given data suggest the following reactions.

$$3Ca+N_2\rightarrow Ca_3N_2$$

$$Ca_3N_2+6H_2O\rightarrow 3Ca(OH)_2+2NH_3$$

$$Ca(OH)_2+CO_2\rightarrow CaCO_3+H_2O$$

It is given that a solution of C becomes "milky" on bubbling carbon dioxide. Therefore, it must be calcium hydroxide which is more soluble than magnesium hydroxide.

How metal calcium is manufactured?

1961935_1725659_ans_8094ea1cb0eb4fe8916a6e958bf42d8c.jpg

Name the element which is invariable bivalent and whose oxide is soluble in excess of NaOH.

Be; BeO dissolved in NaOH.

$$BeO + 2NaOH\rightarrow Na_2[Be(OH)_4]$$

Arrange the following:
$$Sr, Ba, Ca, Mg$$ in order of increasing reducing nature.

1962111_1725624_ans_6d1b0815bb394eb7aa2c2c2aadb8a945.jpg

How does the oxidation potential of the alkaline earth metals change when we move from Be to Ba?

1961927_1725476_ans_38ab20b89c7642a0b81dc6f540ebf578.jpg

Answer with giving reason:
Which is more hydrated?
$$Be^{2+}, Na^+, Ca^{2+}$$

1737025_1725631_ans_e000faa26af846559984767de63c6585.jpg

Give reasons:
$$LiBr$$ has lower melting point than $$LiF$$.

$$Br^{-}$$ ion on account of bigger size than $$F^{-}$$ ion, is more polarisable than $$F^{-}$$ ion. Hence, $$LiBr$$ is more covalent than $$LiF$$ and thus it has lower melting point.

Answer the following:
What makes lithium to show properties different than other alkali metals?

Lithium shows different properties than other alkali metals due to following reasons:

(i) small atomic and ionic size

(ii) high ionisation potential

(iii) high polarizing power

Give reasons:

$$LiCl$$ is soluble in alcohol.

$$LiCl$$ has a significant covalent and ionic character and thus, it is soluble in alcohol.

Give reasons:
$$MgCl_{2}$$ is more than covalent than $$NaCl$$

$$Mg^{2+}$$ ion on account of higher charge than $$Na^{+}$$ ion has greater polarising power. Hence $$MgCl_{2}$$ is more covalent than $$NaCl$$

Match the compounds in List-I with their colour in List-II:

1599073_1726909_ans_6fd6fdefc9a145daa450923a616dde4f.jpg

Answer the following:
Name the alkali metals which form superoxides when heated in excess of air.

Potassium, rubidium and caesium.

Lithium is the only alkali metal that form normal oxides having general formula $$M_2O$$, when heated in excess of air while potassium, rubidium and caesium form superoxides having general formula $$MO_2$$, when heated in excess of air.

Complete and balance the following equations:

$$KO_{2}+H_{2}O\rightarrow \ ......\ +\ O_{2}$$

When potassium is strongly heated with oxygen potassium superoxide is formed $$(KO_2)$$.

Potassium superoxide reacts with hot water to produce potassium hydroxide and oxygen.

$$4KO_2+2H_2O\xrightarrow{t^0C} 4KOH+3O_2$$

Match List I with List II

1663375_1727545_ans_f3be5a5a11ee4ec8b3b2cb9c90263b67.jpg

Match the compounds listed in column-I with the related uses/particulars listed in column-II.

(A) $$3Ca\left(OH\right)_{2}+2Cl_{2}\rightarrow{Ca}\left(OCl\right)_{2}\cdot{Ca}\left(OH\right)_{2}\cdot{CaCl}_{2}\cdot{2H_{2}O}$$ (bleaching powder).

$$Ca\left(OCl\right)_{2}$$ is constituent of bleaching powder.

(B) $$CaSO_{4}\cdot\dfrac{1}{2}H_{2}O$$ is called as plaster of Paris.

(C) $$KO_{2}$$ absorbs $$CO_{2}$$ and gives $$O_{2}$$ gas according to the following reactions; so used as air purifier in submarine.

$$2KO_{2}+CO_{2}\longrightarrow{K_{2}}CO_{3}+\dfrac{3}{2}O_{2}; 2KO_{2}+2H_{2}O\longrightarrow2KOH+H_{2}O_{2}+O_{2}$$

(D) Calcium oxide i.e. quick lime is used for the removal of temporary hardness of water.

$$CaO+H_{2}O\longrightarrow{Ca}\left(OH\right)_{2}; Ca\left(OH\right)_{2}+Ca\left(HCO_{3}\right)_{2}\longrightarrow2CaCO_{3}\downarrow+2H_{2}O$$

$$Ca\left(OH\right)_{2}+Na_{2}CO_{3}\longrightarrow{CaCO_{3}}\downarrow+2NaOH$$ (causticising process).

Name two elements you would expect to show chemical reactions similar to calcium. What is the basis of your choice ?

$$\textbf {Beryllium}$$ and $$\textbf {magnesium}$$ will show similar chemical reactions as calcium. Since these elements belong to same group $$ II $$ and also have two electrons in their outermost shell like calcium.

Name:
(a) A yellow monoxide that dissolves in hot and concentrated caustic alkali.

(b) A white, insoluble oxide that dissolves when fused with caustic soda or caustic potash.

(c) A compound containing zinc in the anion.

(a) $$PbO$$

(b) $$ZnO$$

(c) $$K_2ZnO_2$$

Alkali metals have low ionization energy why?

Alkali metals are present in the periodic table after inert gases. By loosing one electron they gets electronic configuration of inert gas.

Alkali metals are paramagnetic but their salts are diamagnetic. Explain.

Alkali metals contain one upaired electron $$ (ns^1)$$ and hence are paramagnetic. However, during salt formation, this unpaired electron is transferred to the non-metallic atom forming is anion.As a result, salt has paired electrons both in the cation as well as in the anion and hence alkali salts are diamagnetic in nature.

Why alkali metals are normally kept in kerosene oil ?

Alkali metals are normally kept in kerosene oil because in the air they are easily oxidized to oxides which may dissolve in the moisture of the air to form hydroxides or they also combine directly with water vapours present in moisture to form hydroxides.

When is a cation highly polarising ? which alkali metal has the highest polarising power ?

A cation is highly polarising if its charge /size ratio is very high. $$ Li^+ $$ ions has the highest polarising power among the alkali metal ions.

Why is sodium metal kept under kerosene oil ?

$$ Na $$ metal is highly reactive and combines with moisture, $$ O_2 $$ and $$ CO_2 $$ of the air forming $$ NaOH, Na_2O $$ and $$ Na_2CO_3 $$ etc. Therefore, to protect $$ Na $$ from moisture and air,it is kept under kerosene oil.

Why is calcium preferred over sodium to remove the last traces of moisture from alcohol?

Both $$ Na $$ and $$ Ca $$ reacts with water to form their respective hydroxides. But $$ Na $$ readily reacts with alcohol to form sodium ethoxide but $$ Ca $$ reacts only very slowly.

$$ 2C_2H_5OH+2Na \longrightarrow 2C_2H_5ONa+H_2 $$

Therefore, $$ Ca $$ is preferred over $$ Na $$ to remove the last traces of moisture from alcohol.

Why is it that on being heated in excess supply of air , $$ K , Rb $$ and $$ Cs $$ from the superoxides in preference to oxides and proxides?

$$ K^+,Rb^+ $$ and $$ Cs^+ $$ are large cations and superoxide $$ (O_2^- )$$ is larger than oxide $$ (O^{2-})$$ and peroxide $$ (O_2^{2-}) $$ ion. Since a large cation stabilized a large anion, therefore, these metals form superoxides in preference to oxides and peroxides.

Why cesium can be used in photoelectric cell while lithium cannot be ?

Cesium has the lowest while lithium has the highest ionization enthalpy. Hence $$ Cs $$ can lose electrons very easily while lithium cannot.

Among alkali metals in aqueous solution $$ Li^+ $$ ion has the lowest mobility. Why?

Among alkali metals in aqueous solution $$ Li^+ $$ ion has the lowest mobility because of smallest size among alkali metals, $$ Li^+ $$ ions are most highly hydrated in aqueous solution. As a result, among alkali metals, mass of hydrated lithium ions ions is the highest and thus lowest ionic mobility.

Among alkali metals , why is lithium regarded as most apt reducing in aqueous solutions?

Amongst alkali metals, $$ Li^+ $$ has the smallest size and hence the highest hydration energy. In other words, it has the lowest electrode potential $$ (E^o = -3.04 V) $$, i.e, it has maximum tendency to lose electrons and hence is the strongest (most apt) reducing agent amongst alkali metals.

State as to why
(a) A solution of $$ Na_2CO_3 $$ is alkaline
(b) Alkaline metals are prepared by electrolysis of their fused chlorides
(c)Sodium is found more useful than potassium.

i). $$\mathrm{Na}_{2} \mathrm{CO}_{3}$$ when dissolved in water to hydrolysed by it, to form $$\text {NaOH and } \mathrm{H_2} \mathrm{CO}_{3} \text { . Thus, the solution is alkaline }$$ in nature due to prsence of $$O \mathrm{H}^-$$ & $$\mathrm{HCO}_{3}^{-}$$ ions.

$$\mathrm{Na}_{2} \mathrm{CO}_{3}+\mathrm{H}_{2} {O} \longrightarrow \mathrm{HCO}_{3}+\mathrm{{}^-OH}+2 \mathrm{Na}^{+}$$

ii). During electrolysis, of aqueous solution of alkali metal chlorides, hydogen is preferentially evolved than alkaei metal at cathode. Hence, electrolysis of fused alkali metal chlorides is carried out to prepare alkali metals.

ii) Sodium ions are present in blood plasma and intenstitial fluids which surrounds the cell. Potassium ions are

prsent in intracellular fluids. Sodium ions help in transinision of nerve signals, regulate water flow across cell membranes. Hence, sodium is more useful than potassium.

Comment on each of the following observations :
The mobilities of alkali metal ions in aqueous solution are $$ : Li^+ < Na^+ < K^+ < Rb^+ < Cs^+ $$

On moving down the group, the atomic and ionic sizes of alkali metals increases. As the size increases, the extent of hydration decreases. The extent of hydration $$\&$$ ionic mobility are inversely proportional.

Hence, the increasing order of mobilitie of alkali metal is

$$L i^{+}<\mathrm{Na}^{+}<K+<R b^{+}<\mathrm{Cs}^{+}$$

Like lithium in group I beryllium shows anomalous behaviour in groupWrite three such properties of beryllium which make it anomalous in the group?

$$\text { Solution- Anamalous behaviour of berglium (Be), } \\$$

$$\text { 1.) Reaction with air:- All element react with air } \\$$

$$\text { but Be do not, due to formation of oxide layer } \\$$

$$\text { over surface ( surface phenumenon) }$$

$$\text { 2.) Reaction with water: - All metal react with } \mathrm{H}_{2} \mathrm{O} \\$$

$$\text { at different temperature and preduce } \mathrm{H}_{2} \text { but } \mathrm{Be} \\$$

$$\text { do not react with water at any temperature. }$$

$$\text { 3) Nature of oxides and Hydroxides : - All elements } \\$$

$$\text {are basic in nature but BeO and } {Be(OH)_2 } \\$$

$$\text {are amphuteric in nature. }$$

Why are alkali earth metals good reducing agents ?

Alkali metals are good reducing agent because it has only one electron in its outermost orbital. So, its outermost orbital is unstable and they also have low ionization enthalpy so that they easily lose their electron. By losing that one election they get the noble gas configuration.

Calgon is the trade name of ..............

$$\text { Calgon is the trade name of Sodium hexametaphosphate } \\$$

$$\text { It's used for removal of permanent hardness from water and this method is called Calgons method }$$

Give three important uses of each of calcium and magneisum.

$$\text { Biological importance of Calcium (Ca), } \\$$

$$\text { 1.) The presence of Ca is generally found in vast quantities in our bones and teeth. } \\$$

$$\text { 2.) Ca helps in the clotting of blood during an injury. without an adequate amount of calcium, this } \\$$

$$\text {clot will take a long time to form. }\\$$

$$\text { 3.) Muscle contraction in our body is highly influenced by the presence of Ca. } \\$$

$$\text { Biological importance of Magnesium (Mg), } \\$$

$$\text { 1.) Help in proper functioning of enzymes, manyfucturing of enzymes and Proteins } \\$$

$$\text { and also adjusting and balancing of the cholestrol. }\\$$

$$\text { 2.) Help in production of energy within the body, without my source, nutrients can't } \\$$

$$\text { be transformed into ATP. } \\$$

$$\text { 3.) It help in keeping the Human DNA safe and Mg also helps in keeping the } \\$$

$$\text { electrolyte balanced. }$$

Beryllium exhibits some similarities with aluminium. Point out three such properties.

$$\text { Solution:- Point of similarity between Be and Al, } \\$$

$$\text { 1.) The (charge/radius) ratio is nearly the same, this } \\$$

$$\text { is the reason they show similar pattern in properties. } \\$$

$$\text {2.) Both forms co-valent bonds & dissolve in organic } \\$$

$$\text { solvents and both are amphuteric. }\\$$

$$\text {3.) Both forms complex due to precence of vacant orbital, } \\$$

$$\qquad B e F_{2}+2 F^{-} \longrightarrow B e F_{4}^{2-} \\$$

$$\qquad AlF_{3}+3 F^{-} \longrightarrow AlF_{6}^{3-}$$

Give the reason for the following?
Be and Mg do not impart colour to the flame.

Be and Mg both are small in size, due to this the effective nuclear charge will be high, means that their nucleus binds the electrons very strongly. So, the energy of flame is not sufficient to excite the electron of Be & Mg. Hence these elements do not impart any colour.

$$3$$	$$4$$	$$5$$	$$6$$	$$7$$	$$8$$	$$9$$	$$10$$
A	B	C	D	E	F	G	H
$$11$$	$$12$$	$$13$$	$$14$$	$$15$$	$$16$$	$$17$$	$$18$$
I	J	K	L	M	N	O	P

The S-Block Elements - Class 11 Medical Chemistry - Extra Questions

"$$Na^{+}$$ (cation) is smaller than $$Na$$ (atom)."Answer whether the above statement is true or false.If true enter 1, else enter 0.

Out of $$Be^{2+} $$, $$Mg^{+}$$ and $$Ca$$, $$Be^{2+} $$ has maximum IE.If true enter 1, else enter 0.