(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?

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Solution

(a) J.J Thomson discovered the electrons by proposing the plum pudding model. Protons were absent in the model. According to him, the atoms were composed of electrons. This model was like a pudding in which electrons acted as plum and nucleus was the pudding. It has a neutral charge because protons and electrons balance the charge.

(b) No.of protons = no.of electrons = 7
No.of neutrons = mass number - no.of protons = 18 - 7 = 11
Atomic no. = No. of protons = No. of electrons = 7

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(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) 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?