Question

Define covalency.

Answer 1

The combining power or the combining capacity of an element is called its valency.
The number of atoms of other elements with which one atom of an element combines is decided by the valency of that element.
Valency is simply equal to the number of electrons gained, lost or shared by an atom of an element to achieve the nearest noble gas configuration.

For example, the valency of sodium (Na) is 1, magnesium (Mg) is 2, Chlorine (Cl) is 1 etc.

​​​Another example, silicon (atomic number 14) has the following electronic distribution:

K = 2, L = 8, M = 4.

In the outermost shell there are 4 electrons so, the valency of silicon is 4.