How to determine the valence of substances according to the periodic table?

Valence is the ability of atoms to form a certain number of chemical bonds with other atoms.

Most often, valence is associated with the number of unpaired electrons of an atom, which are located at the outer or penultimate to the outer electronic levels.

The highest valency for elements of group A is shown by the number of the group in which the element is located.

For example:

Carbon (C) – highest valence IV,

nitrogen (N) – V;

magnesium (Mg) – II.

For elements of group B (d and f-elements), the valency is most often equal to 1, 2, 3, because almost all of them exhibit metallic properties.