Question

State the main points of the contradiction of Dalton’s atomic theory by the Modern Atomic Theory.

Answer 1

Dalton’s Atomic Theory:
The main postulates of the theory are:

1. Matter consists of small indivisible particles called – atoms i.e. Atom is the basic unit of matter.
2. Atoms of the same element are – alike in all respects i.e. atoms of hydrogen have the same properties as mass, density, and atoms of oxygen are alike in all respects.
3. Atoms of different elements are different from each other.
   i.e. atoms of hydrogen are different from atoms of oxygen.
4. Atom can neither be created nor destroyed.
5. Atoms combine with other atoms in simple whole-number ratio forming compounds or molecules.

Modern atomic theory contradicted Dalton Atomic Theory as:

1. Atom is no longer indivisible as an atom has been divided and has sub-atomic particles
   (a) Protons (b) Neutrons (c) Electrons
2. Atoms of the same element may have different properties
   i.e. i.e.₁¹H, ²₁ H,³₁H Isotopes
3. Atoms of different elements may have the same properties
   i.e. isobars
4. Atoms combine with other atoms may not be in the simple whole-number ratio
   i.e. C12H₂₂O11(Sugar).
5. Atom can be destroyed and converted into energy.