Question

Which of the following postulates of Dalton's Atomic theory became contradictory after the discovery of isotopes.

• A. Matter is made up of tiny indivisible particles called atoms.
• B. Atoms of same elements are identical in all aspects.
• C. Atoms of different elements are different in all aspects.
• D. Atom is the smallest particle or unit of matter which takes part in a chemical reaction.

Answer 1

The correct option is B

Atoms of same elements are identical in all aspects.

Isotopes -They are atoms of an element that have the same atomic number (or the number of protons) but a different number of neutrons.

Postulates of Dalton's Atomic Theory-

1. All matter is made up of tiny particles called atoms.
2. Atoms are indivisible.
3. All atoms of a particular element have identical properties and the same weight.
4. Atoms of different elements have different weights.
5. Atoms of different elements combine in a definite ratio to form the compounds.

The explanation for the correct option:

1. As Isotopes have a different number of neutrons, thus the mass number will also be different for the isotopes.
2. Thus, after the discovery of isotopes, the postulate, “ All atoms of a particular element have identical properties and same weight” becomes Contradictory.

The correct option is b).