Chemical bonding between two or more atoms involves the sharing or transfer of electron density. One key notion in chemical bonding is electronegativity. Ionic bonding involves the complete transfer of electrons for atoms with significantly different electronegativities. Ionic bonding is imagined to involve the formation of two species, one having net positive and the other net negative charge. For atoms with similar or identical electronegativities, covalent bonding involves the sharing of electron density between atoms. The bonding in most molecules is best described as in between these two limits.