The forces between the atoms in a solid can take many forms. For example, a crystal of sodium chloride (common salt) is made up of ionic sodium and chlorine, which are held together by ionic bonds. In diamond or silicon, the atoms share electrons and make covalent bonds. In metals, electrons are shared in metallic bonding. Some solids, like most organic compounds, are held together with "van der Waals forces" coming from the polarization of the electronic charge cloud on each molecule. The dissimilarities between the types of solid come from the differences between their bonding.