H2O

H2O is the chemical formula representing the composition of a water molecule. It shows that each molecule consists of two hydrogen atoms (H) and one oxygen atom (O) bonded together by covalent bonds, meaning the atoms share electrons.

The term H2O is often used interchangeably with the word water, especially in scientific literature. Strictly speaking, H2O denotes a single molecule or a pure substance, whereas water found in natural settings contains dissolved minerals and other impurities.

Molecular structure

The H2O molecule is not linear; the two O–H bonds form an angle of approximately 104–105 degrees. Oxygen attracts electrons more strongly than hydrogen, so the oxygen side carries a partial negative charge and the hydrogen side a partial positive charge. A molecule with this charge distribution is called polar.

This polarity produces hydrogen bonding—an attraction between different water molecules. These bonds account for water's high boiling point and high surface tension compared to other molecules of similar weight, and also for its ability to dissolve many substances.

Physical properties

The molecular mass of H2O is approximately 18 atomic mass units. Under standard conditions, water freezes at approximately 0 degrees Celsius and boils at approximately 100 degrees. A distinctive feature is that ice is less dense than liquid water, causing ice to float—a property with consequences for aquatic and polar ecosystems.

Significance

H2O is the most abundant substance in living organisms. It functions as a medium for transporting nutrients and as a component in biochemical processes such as photosynthesis and respiration. Industries and power generation use water for cooling, washing, and driving turbines.