Water
 A drop of water splashing onto a liquid surface, demonstrating its high surface tension and fluid dynamics.
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| Chemical formula | H2O |
|---|---|
| Molar mass | 18.01528(33) g/mol |
| Melting point | 0 °C (32 °F; 273.15 K) |
| Boiling point | 99.98 °C (211.96 °F; 373.13 K) |
| Density | 997 kg/m3 (at 25 °C) |
| Appearance | Transparent, nearly colorless liquid with a slight blue tint |
Water is an inorganic compound with the chemical formula H2O. It is a transparent, tasteless, odorless, and nearly colorless chemical substance that constitutes the Earth's hydrosphere and the fluids of all known living organisms. It is vital for all known forms of life, despite providing no food energy or organic nutrients.
Each molecule of water contains one oxygen and two hydrogen atoms connected by covalent bonds. At standard ambient temperature and pressure, water is a liquid, but it frequently co-exists on Earth with its solid state, ice, and its gaseous state, water vapor (or steam).
Chemical and Physical Properties
[edit | edit source]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
[edit | edit source]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 bonds.
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
[edit | edit source]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 salts, 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
[edit | edit source]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.
The Hydrosphere and Water Cycle
[edit | edit source]Water covers approximately 71% of the Earth's surface, making the planet a unique celestial body in the Solar System. The total volume of water on Earth is estimated at 1.386 billion cubic kilometers.
- 96.5% of the Earth's water is saline, found in oceans and seas.
- 1.7% is locked in groundwater.
- 1.7% is trapped in glaciers and the ice caps of Antarctica and Greenland.
- Less than 0.3% is accessible surface freshwater found in lakes, rivers, and the atmosphere.
Water moves continually through the water cycle (hydrologic cycle), which involves evaporation from oceans and landmasses, transpiration from plants, condensation into clouds, and precipitation back to the surface.
Biological Importance
[edit | edit source]From a biological perspective, water is the fundamental matrix of life. It acts as a solvent for biochemical reactions, a reactant in photosynthesis, and a structural component maintaining cellular turgor pressure. Without water's ability to act as a medium for cellular metabolism, life as defined by modern science could not exist.
Human Uses
[edit | edit source]Access to safe drinking water and sanitation is recognized as a fundamental human right. Human civilizations have historically flourished along river basins and coastlines. Globally, human water consumption is divided as follows:
- Agriculture (70%): Predominantly used for irrigation to sustain global food production.
- Industry (20%): Utilized as a solvent, a coolant in power stations, and in manufacturing processes.
- Domestic (10%): Used for drinking, sanitation, cooking, and hygiene.