Q.7:- Define valency by taking examples of silicon and oxygen.
The number of electrons gained, lost or shared so as to complete the octet of electrons in valence shell is called valency.
Valency of silicon: It has electronic configuration → 2,8.4
Thus, 4 electrons are shared with other atoms to complete the octet and so its valency = 4
Valency of oxygen : It has electronic configuration →2,6
Thus, It will gain 2 electrons to complete its octet. So its valency = 2