(i) Describe Bohr's model of the atom. How did's Bohr explain the stability of atom?
​(ii) An element has an atomic number of 11 and its mass number is 23. What is the arrangement of electrons in the shells? State nuclear composition of an atom of the element.

(a) Bohr's model of the atom:
Niels Bohr proposed the following postulates regarding the model of the atom.
(i) Only certain orbits known as discrete orbits of electrons are allowed inside the atom.
(ii) While revolving in these discrete orbits, the electrons do not radiate energy.
These discrete orbits or shells are shown in the following diagram



Bohr explained the stability of atom by proposing that electrons revolve around the nucleus in the definite circular paths having fixed energy and while moving in the same orbit they do not lose or gain energy.

(b)
The mass number of the element = 23
The atomic number of the element = 11
Number of electrons = 11
Number of protons = 11
Number of neutrons = 23 - 11
Number of neutrons = 12
Electronic configuration of an element is 2 8 1
And shells used are K L M