Bond formation in carbon dioxide molecule. Illustration of the sharing of electrons (dots and crosses) between two oxygen (O) and one carbon (C) atom to form a molecule of carbon dioxide (CO2). This is an example of covalent bonding, with the two double bonds each formed by two shared electron pairs, each pair consisting of an electron from each atom. The outer electron shell of each atom is shown as a red ring. Carbon dioxide is a gas at room temperature and pressure. For the atoms before the bonds form, see image C028/6474.