Metallic bonding is a type of chemical bonding that arises from the electrostatic attractive force between conduction electrons and positively charged metal ions. Metal atoms lose their valence electrons to a large, delocalized orbital, which leaves the nucleus, and other electrons that are closer to the nucleus, as positively charged cations. The ions form a crystal lattice as they are held together by the negative charge of the delocalized orbital. It may be described as the sharing of free electrons among a structure of positively charged ions, and as a more delocalized version of covalent bonding. Metallic bonding accounts for many physical properties of metals, such as strength, ductility, thermal and electrical resistivity and conductivity, opacity, and lustre.