The molecular formula for silicon dioxide is SiO2. The simplest form of silicon dioxide is SiO2, but SiO2 does not represent a simple molecule (only the ratio of the number of atoms of silicon and oxygen in the silicon dioxide crystal). Pure natural silica crystal, is a hard, brittle, insoluble colorless transparent solid, often used in the manufacture of optical instruments. Silicon oxide does not react with halogens, hydrogen halides, and inorganic acids, but is soluble in hot concentrated bases, molten strong bases, or sodium carbonate.
