In most matter atoms exist close together in aggregates. The inner electrons are held tightly by the nucleus, (i.e. they have very high ionisation energies), but the valence electrons can be attracted to the nuclei of two or more atoms simultaneously. It is this electrostatic attraction of the valence electrons to two or more nuclei that provides the forces which hold atoms together and is the basis of the chemical bond.
This section defines different classes of bonds and the language of depicting them on paper.