Water

Water (H₂O), transparent, odorless liquid that in liquid form and solid form (ice) covers about 74% of the earth's surface. Water is essential to life, which began in the oceans. Water is also humanity's most precious natural resource. The advent of desalination technology has made sea water, which accounts for 97% of the total water on earth, available for use as fresh water. Chemically, water is a compound of hydrogen and oxygen. It is a good solvent for many substances, especially ionic and polar compounds; it is ionizing and itself ionizes to give a low concentration of hydroxide and hydrogen ions. It is thus also a better conductor of electricity than most pure liquids. Water is a polar molecule and shows anomalies due to hydrogen bonding, including contraction when heated from 0°C to 4°C (32°F to 39.2°F). Formed when hydrogen or volatile hydrides are burned in oxygen, water oxidizes reactive metals to their ions and reduces fluorine and chlorine. It converts basic oxides to hydroxides and acidic oxides to oxyacids.