Question

Atomic models have been improved over the years arrange the following atomic models in order of their chronological order

• A. (i),(ii) and (iii)
• B. (ii),(iii) and (i)
• C. (ii),(i) and (iii)
• D. (iii),(ii) and (i)

Answer 1

The correct option is C

(ii),(i) and (iii)

The correct option is(C).

Explanation of the correct option:

Part (ii)

1. Thomson proposed a model in 1899 which looks like a watermelon or Christmas pudding.
2. Thomson proposed that

1. An atom consists of a sphere that is positively charged and the electrons are embedded in it.
2. The atom is electrically neutral as the positive and negative charges balance each other.

Part (i)

Rutherford discovered the atomic model in 1911 by performing gold foil alpha particles scattering experiment.

The main features of Rutherford's model are as follows-

1. The atom consists of the positively charged nucleus at the center as most of the positively charged alpha particles were deflected from the gold foil.
2. The nucleus occupies only a small volume of space as compared to the whole atom since only a small fraction of alpha particles were deflected at small angles from the gold foil.
3. The nucleus is surrounded by negatively charged electrons which revolve around the nucleus just like the planets revolve around the sun in a solar system.

Part(iii)

Neil Bohr discovered the atomic model in 1912.

The main postulates that he made for this model are as follows:

1. atom has a central nucleus surrounded by electrons.
2. The electrons in an atom revolve around the nucleus in certain fixed circular paths which are called orbits or shells.
3. Each orbit has fixed energy called energy levels.
4. The orbit or energy levels are numbered as 1, 2, 3, 4 or K, L, M, N from the nucleus towards the outer side of the atom.
5. The electron does not lose organ energy as long as it remains in a particular orbit.

Hence the correct order of the discovery of the atomic model is (ii),(i), and (iii).