Electron density and traditional structural chemistry of silicates

New rezults of studies on the electron density of silicates are considered in accordance with the traditional structural classification. Precision X-ray diffraction data and results of structure refinement based on high-angle and multipole models are discussed. Bonded radii, charges on atoms and bond ionicities in Si, Al, B and Be tetrahedra are estimated from the deformation electron density maps in relation to the electronic structures of the atoms and their electronegativities. New possibilities for the solution of problems of isomorphism, for investigations on hydrogen bonds and for the classification are demonstrated. It is noted that the electron density distributions allow one to consider fundamentals of traditional structural chemistry of silicates on the electronic level. For selected compounds, the results of experimental studies of the electron density and of quantum-chemical calculations are compared. The bibliography includes 97 references.