Bond formation, hydrogen chloride molecule. Illustration of the sharing of electrons (dots and crosses) between a hydrogen atom (H) and a chlorine atom (Cl) to form a molecule of hydrogen chloride (HCl). This is an example of covalent bonding, with the single bond formed by a shared electron pair consisting of an electron from each atom. The outer electron shell of each atom is shown as a red ring. Hydrogen chloride is a gas at room temperature and pressure. For the atoms before the bonds form, see image C028/6478.