Water
Molar mass: 18.015 g/mol · Class: Covalent compound
Elements: hydrogen, oxygen
Structure
Each water molecule has one oxygen bonded to two hydrogens in a bent shape, with a bond angle of about 104.5 degrees. The oxygen pulls electrons toward itself, making the molecule polar: the oxygen end is slightly negative and the hydrogen ends slightly positive. These partial charges let water molecules form hydrogen bonds with each other.
Properties
Liquid at room temperature with an unusually high boiling point of 100 °C
Excellent solvent for ionic compounds and polar molecules
Expands when it freezes, so ice floats on liquid water
High specific heat capacity that moderates climate
Applications
Solvent for chemical reactions and industry
Drinking water and sanitation
Coolant in power plants and engines
Agriculture and irrigation
Pure water is safe, but never assume any clear liquid is water: many toxic chemicals look identical. Flood water and untreated water can carry pathogens; boiling or proper treatment is needed before drinking.
Data source: IUPAC standard atomic weights 2021; molar mass computed from H2O