Chemical Formulae

Valence refers to the number of electrons an atom can either gain, lose, or share to achieve a stable, full outer electron shell. It determines how an atom interacts with other atoms during chemical reactions. The valence electrons are the electrons in the outermost energy level of an atom.

For example, carbon has a valence of four because it can share or bond with up to four other atoms. Understanding valence is crucial in predicting the types of chemical bonds that atoms can form.

In the main groups of the periodic table, the valence can vary between 1 and 7, but in most elements it usually ranges between 1 and 4. Atoms are called monovalent, divalent, trivalent or tetravalent according to the number of bonds they can form.

​For example, sodium and fluorine are monovalent (i.e. they form one bond), calcium and oxygen are divalent (two bonds), nitrogen is trivalent (three bonds), and carbon and sulphur are tetravalent (four bonds).

Carbon combined with oxygen forms two types of compounds: divalent carbon and oxygen develop into carbon monoxide (CO), while tetravalent carbon and oxygen develop into carbon dioxide (CO2).