
 The atom of an element has 4 electrons in its Mshell. What is the atomic number of that element?
 If Z = 3, what would be the valency of the element? Also name the element.
 State the three rules proposed by Bohr and Bury, regarding the distribution of electrons in different orbits of an atom.

 The maximum number of electrons occupied by K and Lshells are 2 and 8 respectively and there are 4 electrons in the Mshell of the atom. Therefore, the electronic configuration of this element is 2, 8, 4.
The total number of electrons = 2 + 8+ 4 = 14. In a neutral atom, number of electrons is equal to the number of protons. Therefore, the atomic number of this element is 14.
 As Z = 3, therefore electronic configuration =2,1. It has one valence electron. Therefore, its valency is equal to one. The element having atomic number three is lithium (Li).The three rules are:

 The maximum number of electrons present in a shell is given by the formula 2n2, where n is the orbit number or energy level, i.e. 1, 2, 3 …, therefore, the maximum number of electrons in
different shells are as follows :
First orbit or Kshell = 2 x 1^{2} = 2
Second orbit or Lshell = 2 x 2^{2} = 8 and so on.
 The maximum number of electrons that can be accommodated in the outermost orbit is 8.
 Electrons are not accommodated in a given shell, unless the inner shells are filled, i.e. shells are