Define valency by taking examples of silicon and oxygen.

Explanation

The combining capacity of an atom of an element is known as its valency . The number of electrons gained , lost or shared so as to make the octet of electrons in the outermost shell of an atom of an element gives us directly the combining capacity of the element .

Valency of oxygen is 2 because it can complete its octet by gaining 2 electrons . Valency of silicon is 4 because it can loose , gain or share 4 electrons to complete its octet .