Explain and arrange the following statements in the correct chronological. Class 9

Explain and arrange the following statements in the correct chronological. Class 9

Question 1.

Explain and arrange the following statements in the correct chronological order to show how atomic models have evolved over time. Class 9

(i) Bohr’s model proposed that electrons move in fixed orbits around the nucleus, each with a definite energy.

(ii) Thomson’s model depicted the atom as a 'plum pudding' with electrons embedded in a sphere of positive charge.

(iii) Rutherford’s model proposed that atoms have a dense central nucleus.

(iv) Dalton’s model described atoms as indivisible particles.

Answer:

Correct chronological order and explanations:

1. (iv) Dalton's model (1808): Dalton described atoms as indivisible particles - the fundamental building blocks of matter that cannot be broken down further. This was the first scientific atomic theory, based on experiments of that time.

2. (ii) Thomson's model (1897 onwards): After the discovery of the electron by J. J. Thomson,

he proposed that the atom is a sphere of positive charge with electrons embedded throughout it (plum pudding model). This was the first model to acknowledge that atoms contain smaller charged particles.

3. (iii) Rutherford's model (1911): After the gold foil experiment, Rutherford proposed the planetary model - the atom has a small, dense, positively charged nucleus at its centre, with electrons revolving around it like planets around the Sun. This disproved Thomson's model.

4. (i) Bohr's model (1913): To explain why electrons do not lose energy and fall into the nucleus (a limitation of Rutherford's model), Niels Bohr proposed that electrons move in fixed circular orbits (shells) with definite energies, called stationary states. Electrons do not lose energy while in these fixed orbits.

So the chronological order is: (iv) v→ (ii) → (iii) → (i)