Question

Explain the drawbacks of Dalton's Atomic theory? What did JJ Thompson do to change Dalton's claim? [5 MARKS]

Answer 1

Stating drawbacks:.2.5 Marks
Reasoning out :2.5 Marks

Drawbacks of Dalton's Atomic Theory:

a) Unlike previously stated that atoms are not indivisible particles, but can be further subdivided into protons, neutrons and electrons.
b) The atoms of same elements are not similar, they may vary in mass and density(Isotopes).
c) According to Dalton, atoms of different elements combine in simple whole number ratio to form compounds. This is not seen in complex organic compounds
like sugar $C_{12}{H}_{22}{O}_{11}$. The theory fails to explain the existence of allotropes

Dalton has proposed that atoms were the smallest particles which make up matter. However, Thomson discovered the electron, which was even smaller than an atom!Thomson's experiments with cathode ray tubes helped him to discover the electron (which Dalton did not know about). Dalton thought that atoms were indivisible particles, and Thomson's discovery of the electron proved the existence of subatomic particles.

This ushered in a model of atomic structure referred to as the plum pudding model.



In the figure the cookie dough is positively charged and the chocolate chips (electrons) are negatively charged and scattered randomly throughout the cookie (atom). The positive and negative charges cancel producing a neutral atom.