Editing Water (section)

== Chemical and Physical Properties ==

The molecular structure of water gives it unique physical and chemical properties that strictly dictate the environmental and biological conditions of Earth.

=== Polarity and Hydrogen Bonding ===
Water is a polar molecule. The oxygen atom has a higher [[electronegativity]] than the hydrogen atoms, meaning it attracts the shared electrons more strongly. This creates a partial negative charge near the oxygen atom and a partial positive charge near the hydrogen atoms. Because of this polarity, water molecules attract each other, forming strong intermolecular connections known as [[hydrogen bond]]s.

These hydrogen bonds are responsible for water's unusually high boiling point, specific heat capacity, and high surface tension. The high specific heat capacity of water plays a critical role in regulating the Earth's [[climate]] by buffering large fluctuations in temperature.

=== The Universal Solvent ===
Water is frequently referred to as the "universal solvent" due to its ability to dissolve a wider range of substances than any other known liquid. Substances that dissolve well in water, such as [[salt]]s, sugars, and acids, are termed [[hydrophilic]] ("water-loving"), while those that do not mix well with water, like fats and oils, are termed [[hydrophobic]] ("water-fearing"). This solvency is crucial in biology, as it allows water to transport valuable chemicals, minerals, and nutrients throughout living organisms.

=== Density Anomaly ===
Unlike most substances, which become denser as they freeze, water reaches its maximum density at approximately 4 °C (39 °F). As water cools below this temperature and freezes into ice at 0 °C, its molecules arrange themselves into a rigid, open hexagonal crystal lattice, causing the volume to expand. Consequently, ice is less dense than liquid water, allowing it to float. This anomaly prevents oceans and lakes from freezing solid from the bottom up, preserving aquatic life during colder epochs.