Question

How did J.J Thomson change Dalton’s atomic theory?

Answer 1

Hint: There were few limitations of Dalton’s atomic theory which he failed to explain about the atom which was further explained by J.J Thomson in his model. He explained the atom can be subdivided.

Complete step by step answer:
According to Dalton’s atomic theory, every element present in the space is formed of small particles that cannot be seen through naked eye. These particles were considered as atoms.
The postulates of Dalton’s atomic theory are shown below.
(1) Every matter is made up of fundamental unit called as matter
(2) Matter consists of indivisible particles known as atoms.
(3) Atoms of the same element have similar shape and mass, but differ from the atoms of other elements.
(4) Atoms cannot be created nor be destroyed.
(5) Atoms of the same element can combine in more than one ratio to create two or more compounds.
(6) The atom is the smallest unit that takes part in chemical reaction.
Drawbacks of Dalton’s atomic theory
(1) The fact that atoms are indivisible was wrong. The atom can be further subdivided into protons, electrons and neutrons.
(2) According to Dalton’s theory atoms of the same element are similar in all aspects but the atoms of some element vary in their masses and density.
(3) The theory fails to explain the existence of allotropes.
The J.J Thomson modified the atomic theory and in his theory he defined that the atoms are uniformly packed spheres containing positive charged matter filled with negative charged electrons.
Postulates of J.J Thomson model:
(1) An atom contains a positively charged sphere where electrons are embedded in it.
(2) The atom as a whole is electrically neutral in nature as the negative and positive charges have equal magnitude.

Note:
J.J Thomson compared his model with the water melon. He failed to explain the stability of an atom as his model failed to explain how positive charge holds the negative charge electrons in the atom. He does not explain the scattering of alpha particles by thin metal foils.