Water is a simple inorganic compound composed of two hydrogen atoms covalently bonded to one oxygen atom (H₂O). It exists naturally in three phases—liquid, solid (ice), and gas (vapor)—and is the most abundant liquid on Earth’s surface.
Key Characteristics
| Property | Value / Description |
|---|---|
| Molecular weight | 18.015 g mol⁻¹ |
| Polarity | Highly polar molecule, enabling strong hydrogen‑bonding |
| Density | 1 g cm⁻³ ( liquid at 4 °C) |
| Boiling point | 100 °C (1 atm) |
| Freezing point | 0 °C (1 atm) |
| pH (pure) | ≈ 7 (neutral) |
Why Water Matters
- Universal solvent: Its polarity lets it dissolve a wide range of substances, driving chemical reactions in soils, oceans, and living organisms.
- Thermal regulator: High specific heat capacity (4.18 J g⁻¹ K⁻¹) buffers temperature changes in the atmosphere and in biological systems.
- Biological necessity: All known life uses water for metabolism, transport, and structural functions.
Brief Chemical Perspective
The bent geometry (≈104.5° H–O–H angle) gives water a permanent dipole moment (~1.85 D), which underlies its unique cohesion, surface tension, and solvent capabilities .
References
IUPAC Compendium of Chemical Terminology (Gold Book). “Water.”
United States Geological Survey (USGS). “Water Overview.”
K. S. Pitzer, Thermodynamics of Aqueous Solutions, 2nd ed., CRC Press, 2015.
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