#### Q. 7.     Define valency by taking examples of silicon and oxygen.

The definite combining capacity of an atom of an element, in which electrons are lost, gained or shared with other atoms to complete the octave in the outermost shell is defined as valency.

In other words,

Valency is basically the minimum number of electrons we have to add or remove from or in the outermost shell such that every shell in the atom is completely filled.

And Mathematically,

when the outermost shell of an atom contains 4 or less than 4 electrons, its valency is equal to the number of valence electrons in the outermost shell and when the outermost shell contains more than 4 electrons, the valency of the atom is equal to 8 - no. of valence electrons in the atom.

The valency of Silicon:

Atomic number = 14

Distribution of electron :

K = 2

L = 8

M = 4

number of electrons in outermost shell = 4

Valency = 8 - 4 = 4.

The valency of Oxygen:

atomic number = 8

Distribution of electrons:

K = 2

L = 6

The number of electron in outermost shell = 6

Valency = 8 - 6 = 2