H2O

H2O is the chemical compound consisting of two hydrogen atoms covalently bonded to one oxygen atom. It is a polar molecule with a bent geometry, with a bond angle of about 104.45 degrees. Oxygen is more electronegative, creating a partial negative charge on the oxygen and partial positive charges on the hydrogens. Hydrogen bonding leads to many unique properties that affect its behavior as a solvent and in climate and biological systems.

Physical properties include being a liquid at standard conditions, with familiar transitions to solid ice and water vapor. It freezes at 0°C and boils at 100°C at one atmosphere of pressure. Its density is about 1.0 g/cm3 near 4°C, and it exhibits an unusual density maximum at that temperature, as well as expansion upon freezing. Water has a high specific heat capacity and a large heat of fusion and vaporization, contributing to its role in temperature regulation. Its polarity makes it an excellent solvent for many ionic and polar substances.

Occurrence and role: water is the most abundant liquid on Earth’s surface and is essential for all known forms of life. It occurs in oceans, rivers, lakes, glaciers, groundwater, and the atmosphere, and it drives the hydrological cycle through evaporation, condensation, precipitation, and runoff. Natural water contains various isotopes, including protium (H-1), deuterium (H-2), and tritium (H-3); heavy water (D2O) is used in certain nuclear applications.

Uses and environmental aspects: water is fundamental for drinking, sanitation, agriculture, and numerous industrial processes. It serves as a solvent and medium for chemical reactions and as a cooling and cleaning agent. Safety concerns arise from contamination by pathogens or pollutants, and water quality is regulated by standards to protect health and ecosystems.