Ionic Bonding

Ionic bonds exist when the electrons are transferred from one atom to the other. This is typified by the heteronuclear diatomics such as NaCl. In general ionic bonds are formed when the electronegativity difference (Δχ) between the two atoms is > 1.7. This most commonly occurs when a group I or II metal is bonded to a main group element (groups 3-7).

	For NaCl (Δχ = 2.23), the electron density surface is very contracted around the (blue colored) Na atom indicating very low electron density. The very large electron density volume surrounding the Cl atom indicates an area of high electron density (the red color). This is typical of an ionic compound where the Na atom has lost its valence shell electron to the Cl atom. The compound truly exists as Na+Cl-.		Methyl Lithium is an organometallic compound. Again, the (blue colored) electron density surface is very contracted around the Li atom, indicating the loss of an electron to the carbon atom. The electron density surface around the methyl group is red, indicating a very high electron density. Again, this is indicative of an ionic bond. Again, the compound is best thought of as Li+CH3-.
Sodium Chloride		Methyl Lithium