Question

What is the combining capacity of an atom called?

Answer 1

The combining capacity of an atom is called valency.

The number of bonds that an atom can form as part of a compound is expressed by the valency of atom.

For example, nitrogen forms a number of compounds with hydrogen such as ${\mathrm{NH}}_3$, ${\mathrm{N}}_2{\mathrm{H}}_4$, ${\mathrm{N}}_3\mathrm{H}$in which nitrogen atoms have valencies of $3,2$ and $1/3$ respectively.