Classification Of Elements And Periodicity In Properties - Class 11 Engineering Chemistry - Extra Questions

Write the number of vertical columns in the modern periodic table. What are these columns called?

Elements in the modern periodic table are arranged in 7 periods and 18 groups. The number of vertical columns in the modern periodic table is 18. Vertical columns in the table are called groups.
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How many vertical columns are there in the modern periodic table and what are they called?

There are 18 vertical columns in the modern periodic table which are known as groups. Elements in the same group tend to show patterns in atomic radius, ionization energy and electronegativity. 


Fill in the blanks in the following statements :
The horizontal rows in a periodic table are called .......

The horizontal rows in a periodic table are called Periods .


Write observed electronic configuration of elements from first transition series having half filled d-orbitals.

Electronic configuration of elements from first transition series having half filled d-orbitals
(1) Chromium (Cr) -$$ [Ar] 4s^{1} 3d^{5}$$
(2) Manganese (Mn) -$$ [Ar] 4s^{2} 3d^{5}$$
out of these two chromium shows deflection form its expected $$[Ar]4s^{2}3d^{4}$$ to attain half filled d orbitals i.e.,to attain stability.

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Which is the shortest period in the long form of the periodic table?

First period


How many incomplete periods are there in the long form of the periodic table? 

One period i.e. 7th period 


Which is the longest period in the long form of the periodic table? 

Sixth period


Atomic size and ionic size decreases in I group elements of the modern periodic table if we move downwards.

If the statement is true enter 1 else 0

Two changes in properties of $$I$$ group elements of modern periodic table.
(i)Atomic and ionic size increases on moving downwards.
(ii)Electropositivity and metallic character decreases on moving downwards.


Column II give period to which element in column I, match them correctly.

Above elements are arranged according to their outer most shell.
Hydrogen - $$ 1s^{1}$$
Sodium     - $$1s^{2}2s^{2}2p^{6}3s^{1}$$
Calcium    - $$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}$$
Barium      - $$[Xe]\ 6s^{2}$$.
In sodium, the outer most shell is 3 whereas hydrogen has 1 whereas calcium is 4 and finally barium is 6. Hence we will match $$A$$ to 4, $$B$$ to 1, $$C$$ to 2 and $$D$$ to 3.


What are periods in a periodic table?

What is meant by period number? What does it signify?

Periodic Table: The periodic table is a tabular arrangement of the chemical elements, ordered by their atomic number, electronic configuration, and recurring chemical properties, whose structure shows a periodic trend.

Periods are the row in the periodic table where the elements are arranged.
There are 7 such periods in the periodic table.

All the elements in the period have the same number of atomic orbitals.

For example, Every element in the top row (the $$1^{st}$$ period) has one orbital for its electrons. All the elements in the second row (the $$2^{nd}$$ period) has two orbitals for their electron. 


What are the difference between electron gain enthalphy and ionization energy towards 2 period elements and IIA and VA group elements.

$$IE=$$Group$$II<$$Group$$V$$
$$EA=$$Group$$II<$$Group$$V$$
Since$$,$$ Group$$II$$ has less $${Z}_{eff},$$ hence looses $${e}^{-}$$ easily than Group$$V,$$ non-metals has more $${e}^{-}$$ affinity than metals due to smaller size$$,$$ high $${Z}_{eff}$$ etc than metals$$.$$


Explain the following with suitable examples:
$$12 - 16$$ and $$13 - 15$$ group compounds.

Germanium and silicon are group $$14$$ elements and have a characteristic valence of four and form four bonds as in diamond. A large variety of solid state materials have been prepared by combination groups 13 and 15 or 12 and 16 to stimulate average valence of four as Ge or Si. Typical compounds of group $$13 - 15$$ are lnSb, AlP and GaAs. Gallium arsenide (GaAs) semiconductors have very fast response and have revolutionized semi-conductors devices. $$ZnS, CdS, CdSe$$ and $$HgTe$$ are examples of group $$12 - 16$$ compounds. In these compounds, the bonds are not perfectly covalent and the ionic character depends on the electronegativities of the two elements.


Match the correct ionization enthalpies and electron gain enthalpies of the following elements.

Most reactive non metal is 2 as it has highest negative electron gain enthalpy.

Most reactive metal is 1 as it has least first ionisation enthalpy.

Least reactive elements is 4 as it has high ionisation energy and positive electron gain enthalpy.

Metal forming binary halide is 3 as it as comparable sucessive ionisation energy.


What is the group number, period and block of the element with atomic number $$40$$?

Atomic number=$$40$$
Electronic configuration=$$1s^22s^22p^63s^23p^64s^23d^{10}4p^65s^24d^2$$
Group number=number of $$e^-$$ in $$(n-1)d+$$ no. of $$e^-$$ in valence shell.
$$=2+2=4$$
Period number=Principal quantum number of the valence shell
$$=5$$


In going across a period (R - L) in periodic table the atomic aiv of the atoms___________.


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An elements $$'X'$$ has mass numbers $$35$$ and the number of neutrons, is $$18$$. Identify the group number and period of $$'X'$$ 


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The correct order of increasing electron gain enthalpy with the negative sign for the elements $$O, S, F$$ and $$Cl$$.


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In which period of the periodic table,will an element, be found whose differentiating electron is a 4d electron? 

Fifth period of the periodic table consist of elements in which the differentiating electron is a 4d electron. 


Be and N has an extremely low value of EA (ie. less negative value ) against the trend. Explain 


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Explain the following: 

Why noble gases have positive electron gain enthalpies?

Noble gases have a stable electronic configuration. Hence, it is difficult to add the electron resulting in positive electron gain enthalpy.


Answer the following:
What is hydride gap?


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Name the element of group 17, which has the following properties:

(a) highest electron affinity 

$$Cl$$

Among halogens the electronegativity decreases down the group but the electron affinity of chlorine is greater than that of F, this is  due to the very small size of F atom which results in a very high charge density and consequently strong repulsion between existing valence shell electrons and the entering electron (new coming electron).

Hence chlorine has highest electron affinity.


How would the tendency to gain electrons change on moving from left to right in a period of the periodic table?

On moving from left to right in a period, the tendency of atoms to gain electrons increases. It is because of the increase in effective nuclear charge.


What does each group in the Periodic Table signify?

Each group in the Periodic Table signifies identical outer shell electronic configuration for the elements constituting that group.For example,each element of group 1 has one electron on its outermost shell.


What do you understand by periods in the Periodic Table?

The horizontal rows in the long form of the Periodic Table are called periods.


Define groups.

The vertical columns in the long form of the Periodic Table are called groups.


Give all characteristics of a group.

Characteristics of a group:
1. Valence electrons $$\rightarrow$$ All the elements show same valence electrons in a group.
2. Valence $$\rightarrow$$ Valency of all the elements remains the same in a group.
3. Atomic size $$\rightarrow$$ The atomic size goes on increasing down the group.
4. Metallic character $$\rightarrow$$ In case of metals, the metallic character increases down the group.
5. Non-metallic character $$\rightarrow$$ In case of non-metals, the non-metallic character decreases down the group.


What are 'groups' and 'periods' in the periodic table ?

The vertical columns in the periodic table are called 'groups' and horizontal rows in the table are called periods.


If two non-metallic elements $$X$$ and $$Y$$ have $$L$$ and $$M$$ shells as valence shells, respectively with the same no. of electrons. Then, between $$X$$ and $$Y$$ which one has a greater electron affinity?

As the size of the atom increases, the distance between the nucleus and the last shell which receives the incoming electrons increases. Due to this the force of attraction between the nucleus and the incoming electron decreases and thus the electron gain enthalpy becomes less negative. But there is an exception in the case of L and M shell.

Given that $$X$$ has $$L$$ shells while the $$Y$$ have $$M$$ shells as valence shells, i.e., $$X$$ is smaller in size, but $$Y$$ has greater electron affinity due to high electron-electron repulsion in case of X. 

So, the correct answer is Y.


State whether the statement is True or False:

Across a period there is an increase in electron affinity (EA) value and oxidizing capacity but both properties decrease down the group.

As the size of the elements decreases in a period, the effective nuclear charge on the valence electron increases and this results in an increase in electronegativity. An increasing electronegativity increases the tendency of atoms to accept electrons i.e. electron affinity (EA) and thus the element itself get reduce and act as oxidizing agent. 

Hence, an increase in EA value in a period increases the oxidizing ability/capacity of elements.

Similarly, the electronegativity decreases down the group, thereby decreases the electron affinity down the group i.e. reduces the electron acceptance tendency (EA) and also the oxidizing ability/capacity of elements. 

Hence in a group, EA decreases downward and reduces the oxidizing capacity.


Total number of correct orders of electron affinity values among the following are: 
(a) $$F >  { Cl }$$
(b) $$O >  { O }^{ - }$$
(c) $$ { Ne }^{ + }$$ < F
(d)$$ F > { F }^{ - }$$

(a) Halogens have seven electrons in their valance shells. Therefore, they tend to accept one electron for a stable electronic configuration. It is easier for the halogens to gain electrons to fulfil a stable octet. But the second electron affinity is positive and because of the no tendency to accept an additional electron. The order $$F>Cl$$ is incorrect.

(b) For $$O$$, two electrons are required to complete the octet configuration.  The second electron affinity of oxygen is particularly high because the electron is being forced into a small, very electron-dense space.  We are forcing an electron into an already negative ion. It's not going to go in willingly. EA of  $$O>O^-$$ is correct.

(c)$$Ne^+ $$ is very unstable and tend to accept one electron willingly. EA of $$ Ne^+ < F$$ is incorrect. 

(d) $$F^-$$ do not accept additional electron as the electron goes to the new shell. The EA of $$F>F^-$$ is correct. 
Hence, two orders are correct in the given options.


Differentiating electron in inner transition elements enters the ________ orbital.(s/p/d/f)

In inner transition elements, the differentiating electron enters into f orbitals. 
So these elements are called f-block elements.


Considering their electrons affinities,  it is possible for alkali metals to form an anion like M$$^-$$ where M represents an alkali metal. If true enter 1, else enter 0.

$$M(g)    +    e^-      \rightarrow M^- (g)            \Delta H = - ve$$
  $$ns^1$$                          $$ns^2$$
    $$\uparrow$$                             $$\uparrow \downarrow$$
Since M$$^-$$(g) has paired ns-electrons  it is possible for alkali metals to form an anion lime M where M represents an alkali metal


The group of the element with electronic configurations: $$ { 1s }^{ 2 }{ 2s }^{ 2 }{ 2p }^{ 6 }{ 3s }^{ 2 }{ 3p }^{ 6 }{ 4s }^{ 2 }$$ isIf true enter 1, else enter 0.

From its configuration, it can be seen that
$$ { 1s }^{ 2 }{ ,2s }^{ 2 }{ 2p }^{ 6 }{ ,3s }^{ 2 }{ 3p }^{ 6 },{ 4s }^{ 2 }$$
it has two valence electron so it will belong to second group of table.


The electron affinities of the alkaline earth metals positive. If true enter 1, else enter 0.

$$M(g) + e^- \rightarrow M^- (g)$$
The extra electron must eneter np-subshell, which is effectively shielding the two ns-electrons and the inner electrons. Consequently, the alkaline earth metals have little tendency to pick up an extra electron.And hence  electron affinities of the alkaline earth metals positive


Define electronegativity? How does it differ from electron gain enthalpy ?

Electronegativity is the tendency of an atom to attract the shared pair of electrons towards it in a covalent bond.  It is the property of atoms in molecules.
Electron gain enthalpy is the tendency of an isolated atom in its gaseous state to accept an additional electron to form a negative ion.  It is the property of isolated atoms.


Why do elements in the same group have similar physical and chemical properties?

Explanation:

  • According to modern periodic law, the physical and chemical properties of the elements are periodic functions of their atomic numbers. 
  • The physical and chemical properties depend on the number of valence electrons in an atom.
  • A vertical column in the periodic table of elements is called group. And the elements having a similar outer electronic configuration and having similar valence electrons are placed in the same group. 
  • These valence electrons are responsible for the vast majority of physical properties, chemical properties, and reactivities of the elements. 
  • If the valence shell electronic configuration remains the same within a group, physical and chemical properties tend to remain almost same.

Conclusion:
Elements in a group have the same physical and chemical properties because their atoms have the same number of valence electrons or same valence shell electronic configuration.



What are the factors that affect electron affinity?

(i) Atomic size
(ii) Stability of electronic configuration
(iii) Inter-electronic repulsion
(iv) Screening effect.


Give two reasons, why the number of elements in first period is only 2?

It is because 1st energy level can have only Is orbital which can have two electrons. When $$n = 1$$, then $$1 = 0$$.


True or False
Fifth period of the modern periodic table has 18 elements.

For 5 period, principal quantum number, n = 5 and values of azimuthal quantum number, l = 0, 1, 2, 3

Now, filling of orbitals in sub-shells takes place in order of increasing energy of the sub-shell. Since, energy of 4f sub-shell is higher than 5s sub-shell, the sub-shells available for filling are 5s, 4d and 5p

Total number of orbitals = 1 for 5s + 5 for 4d + 3 for 5p

= 1+ 5 + 3

= 9

Therefore, total number of electrons that can be accommodated in 9 orbitals = 9 * 2 = 18

Hence, the number of elements in 5 period is 18.



True or False
Elements of the same group have same number of electrons for bonding.

The elements in each group have the same number of electrons in the outer orbital. Those outer electrons are also called valence electrons. They are the electrons involved in chemical bonds with other elements. Every element in the first column i.e. group one has one electron in its outer shell.



Fill in the blanks 
_________ period is incomplete.

7th period is considered incomplete because it consists of elements which have not been studied properly yet. Their properties may change after getting sufficient information about them. Thus, we can't give them a permanent recognition as all the elements in the periodic table have many properties and similarities to follow. We've just assigned name to them. Moreover, most of them have been artificially synthesized in the laboratory and are not naturally occurring elements. Not only this, they are also highly unstable elements and not much information is available on them.



Electron affinity of chlorine is more than that of fluorine though electron affinity decreases on descending the group. Explain.

the electron affinity of the fluorine is less than chlorine because the size of fluorine is too small as size decreases from left to right inside period, whereas chlorine has a larger size to accommodate electrons hence electron affinity of chlorine is more than fluorine.


Fluorine has lesser electron affinity value than chlorine. However, fluorine shows the greater ease of formation of $$F^-$$ ion. than chlorine for $$Cl^-$$ ion. How do you justify this?

Due to high electron negativity of Florine atom the tendency to attract electron is high. So, Flourine can easily form $$\overset { \left( - \right)  }{ F } $$ compared to chlorine from $$\overset { - }{ Cl } $$.


Two non-metallic elements X and Y have L and M shells as valence shells respectively with same no. of electrons. Compare the electron affinity values of X and Y.

Two non- metallic elements X and Y have L and M shells as valence shells respectively with same number of electrons. X and Y belong to the group 13 and 17 and period 2 and 3 respectively

As we descend the group, ( from X to Y) , electron affinity generally decreases. 

Reason: 

             Each atom​ ​is larger than the atom above it (this is the atomic radius trend). This means that an added electron is further away from the atom’s nucleus compared with its position in smaller atom. With a larger distance between the negatively charged electron and the positively charged nucleus, the force of attraction is relatively weaker. Therefore electron affinity decreases.



Identify the wrong statements and correct them.
a. Sodium benzoate is used in food preservative
b. Nitric acid is not used as fertilizer in agriculture.
c. Sulphuric acid is called the king of chemicals.
d. The pH of acid is greater than 7.

a. The statement is correct.
b. Nitric acid is used as fertilizer in agriculture.
c. The statement is correct.
d. The pH of acid is less than 7.


Choose the correct answer from the four alternatives given in the brackets:
Number of periods in modern periodic table is _____ .
(7, 17, 8, 18)

In the modern periodic table there are 7 periods, 18 groups and 2 additional series at the bottom of the periodic table. Horizontal rows are called periods and vertical columns are called groups. 


Write down the characteristics and period number of an element having group number 17.

Characteristics:
1. It is called as halogen
2. It belongs to group number 17 
3.Number of valence electrons are 7.
4. It is a non metal
5.The electronic configuration is:
   $$1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{5}}$$
The period number is 3.


Why is the electron gain enthalpy of chlorine more negative than fluorine?

The negative electron gain enthalpy of fluorine is less than that of chlorine. It is due to small size of fluorine atom. As a result, there are strong interelectronic repulsions in the relatively small 2p orbitals of fluorine and thus, the incoming electron does not experience much attraction.


Write down the characteristics of the elements having an atomic number $$17$$.

Characteristics of the elements having an atomic no. $$17\longrightarrow Chlorine (Cl)$$
$$\longrightarrow$$ Electronic configuration of $$Cl:1s^22s^2 2p^63s^23p^5$$
$$\longrightarrow$$ It belongs to $$17^{th}$$ group and $$3^{rd}$$ period.
$$\longrightarrow$$ It has highest $$e^-$$ affinity in its' group.
$$\longrightarrow$$ It is a toxic green colored gas.
$$\longrightarrow$$ It is avery poisonous gas, even a low concentration of it in the air can be fatal.
$$\longrightarrow$$ It does not burn in normal state, but when temperature is increased, it reacts with hydrogen which can cause explosion and release phosgene gas.


Define electron gain enthalpy. Explain, why electron gain enthalpies of some elements are positive? How does electron gain enthalpy vary in the group and in a period?

  • Electron gain enthalpy of an element is the energy released when a neutral isolated gaseous atom accepts an extra electron to form the gaseous negative ion i.e. anion.
  • The atoms of noble gases have completely filled subshell. As a result, there is no room in their valence orbitals and the additional electron has to be placed in an orbital of next higher shell. As a result, energy has to be supplied to add on additional electrons. Thus, they have a positive electron gain enthalpy.
  • As we move down a group, both the atomic size and the nuclear charge increases. But the effect of the increase in atomic size is much more pronounced than the nuclear charge.
With the increase in atomic size, the attraction of the nucleus for the incoming electron decreases. Hence, the electron gain enthalpy becomes less negative.
  • As we move across a period from left to right the atomic size decreases and the nuclear charge increases. Both these factors tend to increase the attraction by the nucleus for the incoming electron. Hence, electron gain enthalpy becomes more and more negative in a period from left to right.


The amount of energy released when an atom in the gaseous state accepts an electron to form an anion. factor which affect electron affinity are: atomic size and Nuclear charge. As atomic radii increases, electron affinity increase. As nuclear charge increase, electron affinity increase. it decrease down a group and increases across a period. Explain.

Electron affinity decreases down the groups and from right to left across the periods on the periodic table because the electrons are placed in a higher energy level far from the nucleus, thus causes a decrease from its pull. However,  since the number of valence electrons increase going down the group, the element should be more stable and have higher electron affinity. As one goes down the period, the shielding effect increases, thus repulsion occurs between the electrons. This is why the attraction between the electron and the nucleus decreases as one goes down the group in the periodic table and electron affinity decreases down a group.


Explain electron gain enthalpies of the noble gases are positive.

  • Electron gain enthalpy of an element is the energy released when a neutral isolated gaseous atom accepts an extra electron to form the gaseous negative ion i.e. anion.
  • The atoms of the noble gases have completely filled subshell. As a result, there is no room in their valence orbitals and the additional electron has to be placed in an orbital of next higher shell. As a result, energy has to be supplied to add on additional electrons. So electron gain enthalpies of noble gases are positive.


For the gaseous reaction, $$K+F \rightarrow K^{+}+F^{-},\Delta H$$ was calculated to be $$19\ kcal$$ under conditions where the cations and anions were prevented by electrostatic separation from combing with each other. The ionization potential of $$K$$ is $$4.3\ eV$$. What is the electorn affinity of $$F$$?

For $$1$$ $$mole$$, $$\Delta H=19$$ $$Kcal=19\times 2.611\times 10^{22}=4.96\times 10^{23}$$ $$eV/mol$$
For $$1$$ $$atom$$, $$\Delta H=\cfrac{4.96\times 10^{23}}{6.023\times 10^{23}}=0.8$$ $${eV/atom}$$
Electron affinity of $$F$$ is $$4.3-0.8=3.476$$ $$eV$$


How will the tendency to gain electrons change as we go from left to right across a period?

Tendency to gain electrons increases as we go from left to right in a period because the effective nuclear charge increases and the atomic radius decreases.


What is the value (including the sign) of the electron gain enthalpy or electron affinity of $$Na^+$$ ion in electron -volts? The first ionization potential for Na is $$118$$ k cal/mole.

$$Na\rightarrow { Na }^{ \\ + }+{ e }^{ - },\quad \quad IE=118\quad kcal/mol\\ { Na }^{ + }+{ e }^{ - }\rightarrow Na\quad ,\quad EA=-118\quad kcal/mol\\ E\cdot A=\left( \cfrac { -118\times { 10 }^{ 3 }\times 4.18 }{ 6.023\times { 10 }^{ 23 }\times 1.6\times { 10 }^{ -19 } }  \right) eV/atom=-5.12\quad eV.$$


Explain the appropriate reason for the following statement:
(a)Size of $$Mg^{2+}$$ is less than Mg.
(b) Electron gain enthalpy of Cl is more than that of F. 

  • Chlorine has higher electron gain enthalpy than fluorine because due to small size of fluorine some energy is utilized in overcoming the force of repulsion among electrons. Hence it has lesser value of electron affinity.


Which of the following pairs of elements would have a more negative electron gain enthalpy? Explain
(a) $$N$$ or $$O$$  (b) $$F$$ or $$Cl$$

$$(a)$$ $$N$$ or $$O$$
$$O$$ has more negative electron gain enthalpy than $$N$$. This is because nitrogen has stable configuration with half filled $$2p$$ orbitals. So, it will resist gain of electrons whereas oxygen has outer electronic configuration of $$2p^4$$. So, it will try to attain stability by gaining $$2$$ electrons.
$$(b)$$ $$F$$ or $$Cl$$
$$Cl$$ has more negative electron gain enthalpy than fluorine. This is because the incoming electron repel each other in fluorine due to small size but in chlorine, the incoming electrons due to not face the electronic repulsion due to large size of chlorine than fluorine.


Although electron gain enthalpy of fluorine is less negative as compared to chlorine, fluorine is a stronger oxdising agent than chlorine. Why?

The electron gain enthalpy of chlorine is more negative than that of fluorine. However, the bond dissociation energy of fluorine is much lesser than that of chlorine. In addition, its small size, the hydration energy of fluorine is much higher than that of chlorine. So, the latter two factors more than compensate for the less negative electron gain enthalpy of fluorine. Thus, fluorine is a much stronger oxidizing agent than chlorine


Observed the Modern Periodic Table and explain the gradation in reactivity of Halogen family .

As studying the Modern periodic table, The group  17 contains the members of the halogen family. 

All of them have the general formula $$X_{2}$$. A gradation is observed in their physical state down the group. 

Thus, fluorine ($$F_{2}$$) and chlorine ($$Cl_{2}$$) are gases. Bromine ($$Br_{2}$$) is a liquid while iodine ($$I_{2}$$) is a solid.




How would the tendency to gain electrons change on moving from left to right in a period of the periodic table? 

The tendency to gain electron increases as we go from left to right in a period because the effective nuclear charge increases and the atomic radius decreases. 
So the protons hold the electrons more tightly thus the loss of electrons become difficult.


Explain the various factors that affect electron affinity.

Electron affinity mainly depend on three factors. They are,
  1. Atomic size
  2. Nuclear charge
  3. Electronic configuration
  • Atomic size $$\rightarrow$$ If the size of the atom is more, greater will be the distance between nucleus and incoming electron. Hence the incoming electron experiences less forces of attraction towards the nucleus of an atom. Therefore, smaller will be electron affinity value.
  • Nuclear charge $$\rightarrow$$ If the nuclear charge increases, the attraction for the incoming electron increases. Hence the electron affinity value increases.
  • Electronic configuration $$\rightarrow$$ Atoms with stable electronic configuration have a less tendency to accept an electron. Hence they possess smaller electron affinity values.
$$\star$$ Note:- Electron affinities are low or almost zero in elements having stable electronic configurations (half filled and completely filled valence subshells) because of the small tendency to accept additional electron.


Arrange the following as property indicated against it:
(a) $$F, Cl, Br$$ and $$I$$ (increasing order of negative electron gain enthalpy)
(b) $$B, Al, Ga$$ and $$In$$ (decreasing order of atomic radius)
(c) $$C, N, 0$$ and $$F$$ (increasing order of second ionization enthalpy) 


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Six elements A,B, C, D, E and F have the following atomic numbers:
A = 12, B = 17, C = 18, D = 7, E = 9 and F = 11
(i) How many elements belong to the third period of the periodic table?
(ii) Identify the elements known as halogens.

$$(i)$$ The electronic configurations of the given elements A, B, C, D, E and F are as follows:
$$\text{A=2, 8, 2}$$
$$\text{B=2, 8, 7}$$
$$\text{C=2, 8, 8}$$
$$\text{D=2, 5}$$
$$\text{E=2, 7}$$
$$\text{F=2, 8, 1}$$
Since the elements A, B, C, and F have three shells thus, they belong to the period third of the periodic table.

$$(ii)$$ The elements B has electronic configuration 2, 8, 7 and E has electronic configuration 2, 7.
$$\bullet$$ Both these elements have 7 electrons in their valence shells. Thus, they belong to group 17.
$$\bullet$$ Since group 17 elements form salts when they react with metals. Thus they are known as halogens.
$$\bullet$$ Here, elements $$B$$ and $$E$$ belong to group 17 thus, they form salts with metals and are known as halogens.





Which of the following elements has most positive electron gain enthalpy?
Fluorine, Nitrogen, Neon

Both nitrogen and neon have positive electron gain enthalpies but neon has much higher positive electron gain enthalpy because of its much more stable inert gas configuration than the less stable exactly half-filled electronic configuration of nitrogen.


An element has its electronic configuration as $$2, 8, 2$$. Now answer the following question:
What is the group of this element ?

In a Group, all elements have the same number of valence electrons.

Number of valence electron = Group number

$$\because$$ Group number = II

(Since $$2$$ electrons present in valence shell).




Arrange the following in increasing order of the property indicated: 

C. N, O and F      (2nd ionisation enthalpy) 

$$ C < N < F < O .$$ Oxygen has highest because of half filled stability after removing the first eletcron. 


Which element has the highest negative electron gain enthalpy value?

Chlorine 

$$Cl + e^- \rightarrow Cl^- + \Delta H$$

Energy evolved in addition of electron is highest for Chlorine because it has highest tendency to accept electron in its outermost shell. 


An element has its electronic configuration as $$2, 8, 2$$. Now answer the following question:
To which period does does this element belong ?

Period number of an element is equal to the number of total shells that contain electrons in the atom.

$$2,\,\,8,\,\,2$$

$$K,L,M$$

$$\therefore$$ Three shells contains electrons.

$$\therefore$$ This element belongs to $$3rd$$ period.


Arrange the following in increasing order of the property indicated: 

F, Cl, Br and I (electron gain enthalpy) 

 Increasing order of electron gain enthalpy is -

$$ I < Br < F < Cl $$

$$Cl + e^- \rightarrow Cl^- + \Delta H$$

Electron gain enthalpy is the energy evolved when an electron is added in the outermost shell.

Energy evolved in addition of electron is highest for Chlorine because it has highest tendency to accept electron in its outermost shell. 


Nitrogen has positive electron gain enthalpy whereas oxygen has negative. However, oxygen has lower ionization enthalpy than nitrogen. Explain.

The outermost electronic configuration of nitrogen $$(2s^2 2p^1_x2p_y^1 2p_z^1)$$ is very stable because p-orbit is half-filled. The addition of an extra electron to any of the $$2p$$ orbitals requires energy as it breaks the stability of N. Oxygen has 4 electrons in 2p orbitals and acquires stable configuration i.e., $$2p^3$$ configuration after removing one electron and complete octet after gaining two electrons. 

So, nitrogen has positive electron gain enthalpy whereas oxygen has negative, however, oxygen has lower ionization enthalpy than nitrogen.


Explain the following: 
Chlorine can be converted into chloride ion easily as compared to fluoride ion from fluorine. 

Chlorine has higher value of electron gain enthalpy as compared to fluorine. So, chlorine can be converted into chloride ion easily as compared to fluoride ion from fluorine.  


Sulphur has more negative electron gain enthalpy than oxygen. 

O has a much smaller size than S. The electron density is high in oxygen and thus, the addition of electron is difficult. So, sulphur has more negative electron gain enthalpy than oxygen. 


Explain the following: 

Why are the electron gain enthalpies of halogens so high? 

An electron is easily accommodated as halogens acquire inert gas configuration after gaining the electron. So, the electron gain enthalpies of halogens are so high.


The atomic numbers of three elements A, B and C are given below:  
Element                       Atomic number
     A                                         5
     B                                         7
     C                                        10
(i) Which element belongs to group 18? 
(ii) Which element belongs to group 15? 
(iii) Which element belongs to group 13? 
(iv) To which period/periods do these elements belong?

(i) Element C (2,8) belongs to group 18.

(ii) Element B (2,5) belongs to group 15.

(iii) Element A (2,3) belongs to group 13.

(iv) These elements belong to 2nd period (2 shells are filled) of the periodic table.


(a) What is meant by (i) a group, and (ii) a period, in a periodic table
(b) How many periods and groups are there in the long from of periodic table
(c) Give two examples each of (i) group 1 elements (ii) group 17 elements (iii) group 18 elements.

(a) 
(i) The vertical columns in a periodic table are called groups.
(ii) The horizontal rows of elements in the periodic table are called periods.

(b) There are seven periods and eighteen groups in the long form of the periodic table.

(c) 
(i) Group1: Lithium and Sodium.
(ii) Group 17: Fluorine and Chlorine.
(iii) Group 18: Neon and Argon.


Find the neutral atom in the periodic table which has the same number of electrons as $$K^+$$ and $$Cl^-$$ What is this number ? 

Atomic number of K is 19 and after losing one electron it becomes $$K^+$$ so number of electron becomes 18

$$Cl$$ atomic number is 17 after gain of  one electron it will have 18 electrons.

In periodic table neutral atom  Argon has atomic number 18 i.e. 18 electrons




(a) What are the periods and group in a periodic table? Give two characteristics of each. 
(b) In terms of electronic configurations explain the variation in the size of the atoms of the elements belonging to the same period and same group. 
(c) Given alongside is a part of periodic table. As we move vertically downward from Li to Fr.  
      (i) What happens to the size of atoms? 
      (ii) What happens to their metallic character?
(d) Name two properties of elements whose magnitudes change when going from top to bottom in a group of the periodic table. In what manner do they change? 
(e) Rewrite the following statement after correction, if necessary: 
Groups have elements with consecutive numbers.

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(a). The horizontal rows of elements in a periodic table are called periods. Characteristics: 
(i) The elements in a period have consecutive atomic numbers.
(ii) The number of elements in period is fixed by the maximum number of electrons which can be accommodated in various shells. 
Characteristics: 
The vertical columns in a periodic table are called group characteristics 
(i) The elements in a group do not have consecutive atomic numbers.
(ii) All the elements in a group have similar electronic configurations and show similar properties.

(b). The size of the atom decreases on moving from left to right in a period. As we move from left to right in a period the atomic number of elements increases which means that the number of protons and electrons in the atom increases. The electronic configuration of the atoms increases in the same shell. Due to large positive charge on the nucleus, the electrons are pulled in more close to the nucleus, and the size of the atom decreases. On going down in a group of the periodic table the atomic size increases due to the increases in atomic shells.

(c). 
(i) The atomic size increases gradually from lithium to francium due to the addition of shell.
(ii) The metallic character increases from lithium to francium.  

(d). On going down in a group of the periodic table, the atomic size and metallic character increases. When we move down from top to bottom in group 1 of alkali metals, the size of atoms increases gradually from lithium to francium. In group 1 of alkali metals lithium is the least metallic element whereas francium is the most metallic element.
 
(e). Periods have elements with consecutive atomic number. 


(a) What is a period in a periodic table? How do atomic structures (electrons arrangements) change in a period with increase in atomic numbers from left to right?

(b) How do the following change on going from left to right in a period of the periodic table?
     (i) Chemical reactivity of elements. 
     (ii) Nature of oxides of elements. 
Give examples in support of your answer.

(a) The horizontal rows of elements in a periodic table are called periods. As we move from left to right in a period, the atomic number of elements increases which means that number of protons and electrons in the atom increases. Due to large positive charge on the nucleus, the electrons are pulled in more close to the nucleus and the size of the atom decreases.

(b).
(i) On moving from left to right in a period of the periodic table chemical reactivity of elements first decreases and then decreases.
Example: In the 3 rd period of elements, sodium is a very reactive element, magnesium is less reactive whereas aluminium is still less reactive in the third period. Now, the phosphorus is quiet reactive, sulphur is still more reactive whereas chlorine is very reactive.

(ii) On moving from left to right in a period, the basic nature of oxides decreases and the acidic nature of oxides increases.
Example: In the 3 rd period of elements, sodium form most basic oxide and Al and Si form amphoteric oxide and S and Cl form acidic oxide.


(a) How does the electropositive character of elements changes on going down in a group of the periodic table ?

(b) State how valency of elements varies (i) in group and (ii) in a period of the periodic table 

(a) On going down in a group of the periodic table the electropositive  character of elements increases.

(b) (i) In a group all the elements have the same valency.

(ii) In a period on moving from left to right the valency of elements first increases from 1 to 4 and then decreases to zero. 


Name the element which is in:
(a) first group and third period.(b) seventeenth group and second period.

(a) Sodium

(b) Fluorine.


How does the number of valence elctrons vary on moving from left to right

(i) in the first period of the periodic table (ii) in the second period of the periodic table.

(i) The number of valence electrons increases from 1 to 2 in the 1 st period of the periodic table.

(ii) The valence electrons increase from 1 to 8 in the 2nd period of the periodic table.


How does electropositive character of elements in a period vary from left to right?


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Which group of elements could be placed in Mendeleev's Periodic Table without disturbing the original order? Give reason. 

Inert gases could be placed in Mendeleev's Periodic Table without disturbing the original order. Noble gases: like Helium, Neon and Argon had been mentioned by various scientists even before Mendeleev. But these gases could be grouped together as noble gases much later than Mendeleev's discovery. Mendeleev used 63 elements till his periodic table because these were the only known elements till his time. However, he was bold enough to leave gaps in his periodic table. lie had predicted that that more elements would be discovered in times to come. Mendeleev's Periodic Table was the first comprehensive attempt to classify elements on the basis of their chemical properties. This is the main reason that new elements could be easily placed in Mendeleev's Periodic Table without disturbing the original order.


(i) Electropositive nature of the element(s) increases down the group and decreases across the period 
(ii) Electronegativity of the element decreases down the group and increases across the period
(iii) Atomic size increases down the group and decreases across a period (left to right) 
(iv) Metallic character Increases down the group and decreases across a period.
On the basis of the above trends of the Periodic Table, answer the following about the elements with atomic numbers 3 to
(a) Name the most electropositive element among them 
(b) Name the most electronegative element
(c) Name the element with smallest atomic size 
(d) Name the element which is a metalloid 
(e) Name the element which shows maximum valency.

(a) Element with 3 as atomic number, i.e. Lithium
(b) Element with 9 as atomic number, i.e. Fluorine 
(c) Fluorine
(d) Boron (5)  
(e) Carbon, valency 4 


What are horizontal rows and vertical columns in a periodic table known as ?

The horizontal rows are known as $$\textbf {periods}$$ and vertical columns in the periodic table are known as $$\textbf {groups.}$$


Correct the statement.
Elements in the same periods have equal valency.

Elements in the $$\textbf {same group }$$ have equal valency.


What is a periodic table ? How many groups and periods does modern periodic table have ?

A tabular arrangement of the elements in groups (vertical column) and periods (horizontal rows) highlighting the regular trends in properties of elements is called a $$\textbf {Periodic Table.}$$

Modern Periodic table has $$ 7 $$ periods and $$ 18 $$ groups.


Name :
Which has higher E.A. fluorine or neon .

Fluorine, since it require one electron to attain noble gas configuration.


State the number of elements in periods $$1$$, period $$2$$ and period $$3$$ of the periodic table. 

Period $$ 1 $$ has $$ 2 $$ elements while period $$ 2 $$ and period $$ 3 $$ have $$ 8 $$ elements each.


Explain why the following is not correct :
Atoms of elements in the same group have the same number of electron(s).

No two elements have the same number of electrons instead atoms of the same elements in the same group have the same number of valence electrons.


What is meant in the periodic tables by:
A period.

Horizontal row in a periodic table are called as periods. 


What is meant in the periodic tables by:
A group

A Group is a set of chemical elements in the same vertical column of the periodic table. The elements in a group have similarities in the electronic configuration of their atoms, and thus they exhibit somewhat related physical and chemical properties. 


Write down the electronic configuration of the following elements from the given atomic numbers. Answer the following question with an explanation.
$$_4Be$$, $$_6C$$, $$_8O$$, $$_5B$$, $$_{13}Al$$
Which is the most electropositive element among these?

$$_4Be$$, $$_6C$$, $$_8O$$, $$_5B$$, $$_{13}Al$$

Electronic configuration of the following elements is:

  • $$_4Be = 2,2$$
  • $$_6C = 2,4$$
  • $$_8O = 2,6$$
  • $$_5B = 2,3$$
  • $$_{13}Al = 2,8,3$$

$$_{13}Al$$ is the most electropositive element among these because $$_4Be$$, $$_6C$$, $$_8O$$, $$_5B$$ belong to the same period, but $$_{13}Al$$ belongs to next period. According to the trend, the electropositive character of an element increases as we move from top to bottom in a group of the periodic table. This happens as the tendency of an atom to lose electrons increases due to a decrease in nuclear charge and an increase in the number of shells.



Write down the word that will correctly complete the following sentences:
The horizontal rows in a periodic table are called ...........

The horizontal rows in a periodic table are called $$\text{Periods}.$$


State two characteristics of groups.

All the elements in a group have the following characteristics:
1. All elements in a group have same number of valence electrons, hence show similar properties.
2. As we move from top to bottom in a group, the atomic radius goes on increasing and there is a slight gradation in properties.


Define groups and periods.

The vertical columns in a periodic table are called groups and the horizontal rows are called periods.


Explain the periodicity of electron gain enthalpy in a group.

Electron gain enthalpy: On moving from left to right, atomic size decreases and effective nuclear charge increases thus, electron gain enthalpy becomes more negative. On moving down the group, atomic size increases thus, electron gain enthalpy becomes less negative.


Give the characteristics of a period.

In a period as we go from left to right:
(a) Valence electrons $$\rightarrow$$ Goes on increasing $$1, 2, 3, 4, 5, 6, 7, 8$$
(b) Valency $$\rightarrow$$ Valency first increases and then decreases $$1, 2, 3, 4, 3, 2, 1, 0$$
(c) Size of atom $$\rightarrow$$ Size of atom goes on decreasing
(d) Metallic character $$\rightarrow$$ Decreases
(e) Non-metallic character $$\rightarrow$$ Increases


Define electron gain enthalpy. Explain the factors affecting it and it periodicity.

Amount of energy released when an electron is added to an isolated gaseous neutral atom is called electron gain enthalpy  . It is denoted $$ \Delta _{eg} H $$
                          
                     $$ A(g) + e^{-} \rightarrow  A^{-}(g) : \Delta _{eg}  H $$

Electron gain enthalpy is measured in electron volts per atom or kJ per mole . Higher energy released in the process of taking an extra electron , the higher will be electron gain enthalpy .

Factors Affecting  electron gain enthalpy :

  •     Effective Nuclear charge is directly proportional to nuclear charge . With increase in effective nuclear charge , electron gain enthalpy increases .
  • Atomic size : Electron gain enthalpy is inversely proportional to atomic size , with increase in atomic size , value of electron gain enthalpy decrease .


Anion has a larger size than the neutral atom.Explain.

The reason for larger size of anion are :
The negative ion is formed by gain of one or more electrons in neutral atom and the  number of electron increase while the magnitude for nuclear charge remains the same .Hence size increases to accommodate the new electron.


Explain the reason that electron gain enthalpy of $$F$$ is less than $$Cl$$ .

Fluorine is the most electronegative elements but still its electron gain enthalpy is less than that of chlorine . It is because of the small size of fluorine . The electron gain enthalpy of an elements is the energy given off when a neutral atom in the gas phase gains an extra electron to from a negatively charged ion . A fluorine atom in the gas phase , for example , gives off energy when it gains an electron to from a fluorine ion . 


Which element has highest electron gain enthalpy in periodic table ?

Chlorine has the highest electron gain enthalpy in the periodic table . As we know that electron enthalpy increases across the period and decrease along the Group .


What is the relation between number of electrons present in the last $$'s'$$ subshell and their group number ?

$$\text{The number of electrons in the outermost}$$ $$'s'$$ subshell $$=$$ $$\text{The group number}$$


What is meant by group and period?

The vertical columns of the periodic table are called groups and the horizontal rows of the periodic table are called periods.


Electron gain enthalpy of fluorine less negative than that of chlorine. Explain.

Even though Fluorine has the highest electronegativity among all the elements and it should have the highest electron gain enthalpy among all the halogens but this is an exception and chlorine has higher electron gain enthalpy than Fluorine. 

The negative electron gain enthalpy of fluorine i.e. $$F$$ is less than that of chlorine i.e. $$Cl$$. It is due to the small size of the fluorine atom. As a result, there are strong interelectronic repulsions in the relatively small $$2p$$ orbitals of fluorine and thus, the incoming electron does not experience much attraction.



What is the significance of the terms 'isolated gaseous atom' and 'ground state' while defining the ionization enthalpy and electron gain enthalpy?

When an atom is free from other atoms in gaseous state, it is called isolated gaseous atom. No energy is required to separate it further from other atoms. 

The lowest energy state possible for an atom is the ground state.


Why are the electron gain enthalpies of $$Be$$ and $$Mg$$ are positive?

"Electron gain enthalpy is energy released when one mole of electrons is added to gaseous atoms of an element".
Positive electron gain enthalpy means energy needs to be supplied so that an electron can enter the atom.
$$Be$$ and $$Mg$$ are electropositive metallic elements, which become unstable on adding electrons.
$$\therefore $$ Electron gain enthalpy of $$Be$$ and $$Mg$$ care positive.


What is electron affinity and how it depends on atomic size, effective nuclear change and screening factor?

$$e^-$$ affinity is the amount of energy required to add a $$e^-$$.
$$e^-$$ affinity value increases with effective nuclear charge. With the increase in effective nuclear charge, attraction increases thereby increasing $$e^-$$ affinity. Also, as screening/shielding effect increases, electron affinity decreases as the incoming $$e^-$$ has not much attraction with the nucleus.


Be and N has extremely low value of EA against the trend. Explain.

$$Be\longrightarrow 1s^22s^2$$
$$N\longrightarrow 1s^22s^22p^3$$
Both of them are present in the stable form. 
$$\therefore$$ addition or removal of $$e^-$$ in these stable element is difficult. Hence they have low value (less negative value) of $$EA$$ value.


The first IP of lithium is $$5.41eV$$ and electron affinity of $$Cl$$ is $$-3.61eV$$. Calculate $$\Delta H$$ in $$kJ$$ $${mol}^{-1}$$ for the reaction:
$${Li}_{(g)}+{Cl}_{(g)}\rightarrow {Li}_{(g)}^{+}+ {Cl}_{(g)}^{-}$$

First step refers to the image$$.$$
$$\Delta H=(1.8\times1.602\times{10}^{-19}\times6.023\times{10}^{23}\times{10}^{-3})=173.6 $$ $$kJ/mol.$$

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Give appropriate reasons
Fluorine has less gain enthalpy than chlorine yet it taken compunds. Why?


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Define the term 'electron affinity'. State its unit.


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Discuss the factors affecting electron gain enthalpy and the trend in its variation in the periodic table.


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Class 11 Engineering Chemistry Extra Questions