Physical property of SiO2.

Due to the tetrahedral structure, the melting point of silicon dioxide is very high. Strong silicon-oxygen covalent bonds break down at very high temperatures, close to 1700o C. In addition, silicon dioxide is very tough, which is also associated with a strong covalent bond between silicon and oxygen. Due to the lack of free electrons in the molecular structure, silicon dioxide is a very poor conductor of electricity and acts as an insulator. Silicon dioxide is insoluble in water and in all organic solvents. However, it is soluble in alkalis and hydrofluoric acid.