The empirical bond strength of the SiO bond correlates with the value of the electron density at the bond critical point calculated for a large number of silicates and observed for the silica polymorphs stishovite and coesite. The greater the bond strength, the greater the localization of the electron density at the critical point, the shorter the bond, and the greater the covalent character of the bonded interaction. Bond strength and resonance bond number are considered to represent similar properties of the electronic structure of the bond.