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CBSE Questions for Class 9 Chemistry Structure Of The Atom Quiz 8 - MCQExams.com
CBSE
Class 9 Chemistry
Structure Of The Atom
Quiz 8
Which of the following is one of the postulates of Rutherford's theory?
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Electrons continuously lose energy
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Electrons move in a spiral path around the nucleus
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Electrons revolve in a specific path around the nucleus
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Electrons revolve in a stationary orbit
Explanation
According to Rutherford's theory, el
ectrons revolve in a specific path around the nucleus.
An atom has no net charge or they are electrically neutral because electrons are negatively charged and the densely concentrated nucleus is positively charged.
Hence, option C is correct.
For an element with atomic number 19, the 19th electron will occupy:
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$$L$$-shell
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$$M$$-shell
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$$N$$-shell
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$$K$$-shell
Explanation
Atomic number=$$19$$
Electrons per shell $$\longrightarrow 2,8,9$$
Maximum Electrons in $$K=2$$
Maximum Electrons in $$L=8$$
Maximum Electrons in $$M=18$$
$$\therefore 19^{th}$$ electron will occupy $$M-$$shell.
Hence, option $$B$$ is correct.
The particle used by Rutherford in
$$\alpha$$
-ray scattering experiment was__________.
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neutron
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electron
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helium nuclei
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X-rays
Explanation
Rutherford used $$\alpha$$-particles for scattering experiment. The $$\alpha-$$particles are Helium nuclei $$\left( { He }^{ 2+ } \right) $$. Thus the answer for given question is Helium nuclei.
The size of the nucleus is approximately:
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$$10^{-18}$$ m
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$$10^{-10}$$ m
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$$10^{-8}$$ m
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none of these
Explanation
The approximate size of the nucleus is of the order $${ 10 }^{ -15 }m$$. As there is no option of $${ 10 }^{ -15 }m$$, the correct option is 'D'-none of these.
The nucleus of the hydrogen atom is called as:
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neutron
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electron
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proton
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nucleons
Explanation
The nucleus of a hydrogen atom is called a proton as it has only one proton in it. Thus the correct answer is option $$C$$.
Rutherford's scattering experiment is related to
:
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neutrons
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atom
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electron
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nucleus
Explanation
$$\bf{Hint:}$$ He
concluded that almost all the atomic matter was concentrated in a tiny volume.
$$\bf{Explanation:}$$
Rutherford defined that an atom consists of a large space where α− particles pass through, but only at a small region they are deflected. This region is known as a nucleus.
In this experiment, a bean of an alpha particle is placed on gold foil and the ejected particles are captured on the fluorescent screen. from this experiment some of the conclusions can be drawn as;
1. Most of the particles remain undeflected so atoms consist of large space empty.
2. Some of the particles are deflected by small angles that mean the nucleus is positively charged.
3. Very few particles are deflected by large angles and travel back so that means the nucleus consists of all of the atom's mass.
So it gives information related to the nucleus.
$$\bf{Final \ answer:}$$ Option $$D$$
Which of the following was not proposed by Thomson?
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The negative and positive charges are equal in magnitude
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The electrons revolve around the nucleus in circular paths
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The electrons are embedded in a positive sphere
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Atoms are electrically neutral
Explanation
The electrons revolve around the nucleus in circular paths was first proposed by Rutherford, not by Thomson.
Oxygen atom has an atomic mass of 16u and eight neutrons in its nucleus. What is its atomic number?
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4
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12
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8
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6
Explanation
The atomic number of oxygen is 8.
The mass of an atom is given by the sum of the masses of protons and neutrons present in the nucleus. Also, atomic number is the number of protons present in the nucleus.
Since the number of neutrons present in oxygen is 8 and the given mass is 16.
Therefore, the number of neutrons will be equal to $$8$$ i.e. $$16-8$$.
What do you think would be the observation if the $$\alpha$$
-particle scattering experiment is carried out using a foil of a metal other than gold?
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$$\displaystyle \alpha $$ particles would deflect by the foil by large angles
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Most of the fast moving $$\displaystyle \alpha $$ particles would not pass straight through the metal foil
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There would be no change in the observation
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All particles would appear rebound
Explanation
If $$\alpha $$-particle scattering experiment is carried out using a foil of any metal as thin as gold foil used by Rutherford, there would be no change in observations. But since other metals are not so malleable so, such a thin foil is difficult to obtain. If we use a thick foil, then more α-particles would rebound.
Hence, the correct option is $$D$$
This diagram represents the atomic structure of which element?
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Fluorine
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Chlorine
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Carbon
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Oxygen
Explanation
The total number of electrons present in carbon is 6. The distribution of electrons in carbon atom is given by:
First orbit or K shell $$=\displaystyle 2\left( 2{ n }^{ 2 }=2\times 1=2 \right) $$
Second orbit or L shell $$\displaystyle = 4\ (6-2=4)$$
The following diagram represents the atomic structure of which element?
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Fluorine
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Chlorine
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Carbon
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Oxygen
Explanation
The total number of electrons present in fluorine is 9. The distribution of electrons in fluorine atom is given by:
First orbit or K shell $$=\displaystyle 2\left( 2{ n }^{ 2 }=2\times 1=2 \right) $$
Second orbit or L shell $$=\displaystyle 7(9-2=7)$$
Its electronic configuration will be $$2,7$$
For Chlorine, (atomic number 17), the electronic configuration will be $$2,8,7$$
For Carbon, (atomic number 6), the electronic configuration will be $$2,4$$
For Oxygen, (atomic number 8), the electronic configuration will be $$2,6$$
Hence option $$A$$ is correct.
Which of the following statement is incorrect according to Thomson's model of an atom?
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The electrons, in a sphere of positive charge, were like currants (dry fruits) in a spherical Christmas pudding.
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The positive charge in the atom is spread all over like the red edible part of the watermelon.
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The electrons are studded in the positively charged sphere, like the seeds in the watermelon.
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The protons are studded in the positively charged sphere, like the seeds in the watermelon.
Explanation
Thomson proposed the model of an atom be similar to that of a Christmas pudding.
The electrons, in a sphere of positive charge, were like currants (dry fruits) in a spherical Christmas pudding.
One can also think of a watermelon, the positive charge in the atom is spread all over like the red edible part of the watermelon, while the electrons are studded in the positively charged sphere, like the seeds in the watermelon.
Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?
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4
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2
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8
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6
Explanation
Helium has 2 neutrons.
The mass of an atom is given by the sum of the masses of protons and neutrons present in the nucleus. The number of protons present in helium is 2 and, the given mass is 4. Therefore, the number of neutrons will be equal to $$2$$ that is $$4-2.$$. Hence option B is correct.
Which of the following are features of Rutherford nuclear model of an atom?
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There is a positively charged center in an atom called the nucleus.
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The electrons revolve around the nucleus in circular paths.
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The size of the nucleus is very small as compared to the size of the atom.
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All of the above
Explanation
Rutherford put forward the nuclear model of an atom, which had the following features:
There is a positively charged center in an atom called the nucleus.
The electrons revolve around the nucleus in circular paths.
The size of the nucleus is very small as compared to the size of the atom.
Thomson proposed that:
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an atom consists of a positively charged sphere and electrons are embedded in it.
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negative and positive charges are equal in magnitude. So that atoms as a whole are electrically neutral.
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Both $$A$$ and $$B$$
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None of above
Explanation
Thomson proposed that :
An atom consists of a positively charged sphere and the electrons are embedded in it. Thus, the atom is visualised as pudding or cake of positive charges with raisins (electrons) embedded into it. Hence it is raisin pudding model or watermelon model.
The negative and positive charges are equal in magnitude. So that atom
as a whole
is
electrically neutral.
Which of the following observations were obtained from $$\alpha$$-particle scattering experiment?
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Most of the fast moving $$\alpha$$-particles passed straight through the gold foil
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Some of the $$\alpha$$-particles were deflected by the foil by small angles
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One out of every 12000 particles appeared to rebound
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All of the above
Explanation
Ernest Rutherford performed an experiment to know the arrangement of electrons within an atom. In this experiment, fast-moving alpha particles were made to fall on a thin gold foil (100 nm thickness). The $$\alpha$$-particles are doubly charged helium ions. It was expected that $$\alpha$$-particles would be deflected by subatomic particles in the gold atom. Since $$\alpha$$-particles were much heavier than protons, he did not expect to see large deflections.
But, the $$\alpha$$-particle scattering experiment gave totally unexpected results.
The following observations were made:
(i) Most of the fast-moving -particles passed straight through the gold foil.
(ii) Some of the -particles were deflected by the foil by small angles.
(iii) Surprisingly one out of every 12000 particles appeared to rebound.
Atoms react to achieve an octet in the outermost shell. This is achieved by
:
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sharing electrons
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gaining electrons
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losing electrons
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all of the above
Explanation
Atoms react to achieve an octet in the outermost shell. This can be done by sharing, gaining or losing electrons.
What is the distribution of electrons in nitrogen atom?
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$$2, 4$$
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$$2, 5$$
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$$2, 6$$
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$$2, 2$$
Explanation
The total number of electrons present in nitrogen atom is $$7$$.
The distribution of electrons in nitrogen atom is given by:
First orbit or $$K$$ shell $$=\displaystyle 2\left( 2{ n }^{ 2 }=2\times { 1 }^{ 1 }=2 \right) $$
Second orbit or $$L$$ shell $$=\displaystyle 5 (7-2=5)$$
Hence, option B is correct.
What is the distribution of electrons in an oxygen atom?
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(2, 4)
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(2, 8)
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(2, 6)
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(2, 10)
Explanation
The total number of electrons present in oxygen is $$8$$.
Therefore, for $$O$$ electron configuration will be $$1s^22s^22p^4$$.
The distribution of electrons in oxygen atom is given by:
First orbit or $$K$$ shell $$=\displaystyle 2\left( 2{ n }^{ 2 }=2\times { 1 }^{ 1 }=2 \right) $$
Second orbit or $$L$$ shell $$=\displaystyle 6(8-2=6)$$
Which of the following atom has a valency of three?
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Magnesium
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Fluorine
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Aluminium
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Carbon
Explanation
Aluminium with three valence electrons has a valency = $$3$$
Fluorine has seven valence electrons and has a valency = $$1$$
Magnesium has two valence electrons and has a valency = $$2$$
Carbon has four valence electrons and has a valency = $$4$$
So, option C is correct.
The following diagram represents the atomic structure of which element?
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Fluorine
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Neon
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Argon
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Sulphur
Explanation
The atomic structure of an element represents the distribution of electrons in different atomic orbitals. Using the atomic structure, we can find out the atomic number. As every element has a unique atomic number, we can identify the element from its atomic number.
In the given structure, the total number of electrons present is 18, and the distribution is (2, 8, 8). So, the element is Argon, and option C is correct.
What is the distribution of electrons in a magnesium atom?
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(2, 8, 1)
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(2, 8, 2)
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(2, 8, 3)
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(2, 8, 4)
Explanation
The total number of electrons present in Magnesium atom is 12.
The distribution of electrons in magnesium atom is given by:
First orbit or K shell $$=\displaystyle 2\left( 2{ n }^{ 2 }=2\times { 1 }^{ 1 }=2 \right) $$
Second orbit or L shell $$=\displaystyle 8\left( 2\times { 2 }^{ 2 }=8 \right) $$
Third orbit or M shell $$=\displaystyle 2(12-2-8=2)$$
If the K and L shells of an atom are full, then what will be the total number of electrons in the atom?
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12
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8
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10
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16
Explanation
The maximum number of electrons in first orbit or K-shell will be $$\displaystyle 2\times { 1 }^{ 2 }=2$$
and second orbit or L-shell will be $$\displaystyle 2\times { 2 }^{ 2 }=8$$. Hence, if K and L shell is full, the total number of electrons in the atom will be 2+8 = 10.
What is the valency of fluorine atom?
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7
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1
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3
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6
Explanation
The fluorine atom has 7 electrons in the outermost shell and its valency could be 7. But it is easier for fluorine to gain one electron instead of losing seven electrons.
Hence, its valency is determined by subtracting seven electrons from the octet and this gives you a valency of one for fluorine.
Which of the following atom doesn't have its valency as one?
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Lithium
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Hydrogen
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Magnesium
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Sodium
Explanation
Lithium, hydrogen, and sodium all generally exhibit a valency of one. On the other hand, magnesium has two electrons in its outermost shell and exhibits a valency of two.
So, the correct option is C.
What is the valency of sulphur atom?
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2
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3
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1
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4
Explanation
The sulphur atom has 6 electrons in the outermost shell, and its valency could be 6. But it is easier for sulphur to gain two electrons instead of losing six electrons.
Hence, its valency is determined by subtracting six electrons from the octet and this gives a valency of two for sulphur.
In Rutherford's gold foil experiment, most of the alpha particles:
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passed straight through the gold foil
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were absorbed by the gold foil
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were deflected by the gold foil
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None of the above
Explanation
In this experiment, most of the alpha particles passed straight through the gold foil. Only some particles were deflected.
Hence, it was concluded by Rutherford that the atom consists of large empty space and
the positive
charge is confined to a very little
space in the atom.
"The atom as a whole is electrically neutral", is a statement proposed by which atomic model?
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Thomson's atomic model
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Goldstein's atomic model
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Chadwick's atomic model
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None of the above
Explanation
Thomson proposed that :
An atom consists of a positively charged sphere and the electrons are embedded in it. Thus, the atom is visualized
as a pudding or cake of positive charges with raisins (electrons) embedded into it. Hence it is the raisin pudding model or watermelon model.
The negative and positive charges are equal in magnitude. So that atoms
as a whole
are
electrically neutral.
What is the valency of chlorine atom?
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2
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3
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1
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4
Explanation
The chlorine atom has $$7$$ electrons in the outermost shell. Losing 7 electrons to obtain the stable electronic configuration is difficult. Instead chlorine gains one electron to achieve the octet state. Therefore, its valency is 1.
Thomson's model was rejected because
:
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it was not clearly specified in detail
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it could not explain how both positively and negatively charged particles protect their identity being together
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it does not explain any repulsions which might result since all the positive charges are together in an cluster and same is the case with negative charges as well
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All of these
Explanation
Thomson's model was rejected because
it could not explain how both positively and negatively charged particles protect their identity being together.
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