(a) Describe Thomson's model of the atom. Which subatomic particle was not present in Thomson's model of the atom?(b) The mass number of an element is 18. It contains 7 electrons. What is the number of protons and neutrons in it? What is the atomic number of the element?

(a) J.J Thompson proposed a model of the atom that is similar to a watermelon.
The electron in the sphere was considered as seeds in watermelon. 
He proposed that:
  1. The atom consists of a positively charged sphere and the electrons are embedded in it.
  2. The negative and positive charges are equal in magnitude so the atom is electrically neutral.
This model did not tell us about the presence of neutrons in the atom.

(b) Mass no. is 18
No. of electrons is 7
Hence,
No. of protons = 7
No. of neutrons = 18 - 7 = 11
 Atomic no. = 7

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Updated on: 10-Oct-2022

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