Sodium chloride. Computer model of a plane of the crystal lattice of common salt (sodium chloride), a chemical which is found widely in nature and is used as a food flavouring. Small spheres represent positively- charged sodium ions, and large spheres are negatively- charged chloride ions. Sodium chloride crystals consist of rows of such planes, each arranged so that the chloride ion in one plane fits over the sodium ion in the one beneath it. Each positive ion therefore has six negatively-charged nearest neighbours, and vice versa. The electrostatic attraction holding these nearest neighbours together makes the crystal strong but brittle.