H2O — Water
Water (H₂O) is a neutral, tasteless, colorless, and odorless liquid that is essential for all forms of life. It exists naturally in all three states—solid (ice), liquid (water), and gas (water vapor)—and is often called the universal solvent due to its remarkable ability to dissolve a wide range of substances.
Interactive 3D Molecular Structure — H2O
Properties
| Chemical Formula | H₂O |
|---|---|
| Molecular Mass | 18.015 g·mol⁻¹ |
| Physical State | Liquid at room temperature (25°C) |
| Melting Point | 0°C (273.15 K) |
| Boiling Point | 100°C (373.15 K) |
| Density | 1 g·cm⁻³ at 4°C |
| pH | 7 (neutral at 25°C) |
| Odor | Odorless |
| Taste | Tasteless |
| Color | Colorless in small quantities, blue in large masses |
| Polarity | Polar molecule due to bent geometry and electronegativity difference |
| Bond Angle | ≈ 104.5° |
| Type of Bond | Covalent bond with hydrogen bonding between molecules |
| Dielectric Constant | ≈ 80 at 20°C (high, indicating strong solvent capacity) |
Structure and Composition of Water
Water is composed of two hydrogen atoms and one oxygen atom linked by covalent bonds. The molecule has a bent or V-shaped geometry with a bond angle of approximately 104.5°. Due to the higher electronegativity of oxygen, the shared electrons are pulled closer to oxygen, making the molecule polar.
\( \text{H}_2\text{O} \)
The oxygen atom carries a partial negative charge (δ⁻), and the hydrogen atoms carry partial positive charges (δ⁺), leading to strong hydrogen bonding among water molecules.
Physical Properties of Water
Water shows several unique physical properties because of hydrogen bonding:
- High specific heat capacity: Helps regulate Earth's temperature.
- High surface tension: Allows insects to walk on water.
- Maximum density at 4°C: Ice floats on liquid water, ensuring aquatic life survival in winter.
- High latent heat of vaporization: Useful in temperature regulation in living organisms.
- Excellent solvent: Dissolves ionic and polar substances easily.
Chemical Properties of Water
Water participates in many chemical reactions, acting as both an acid and a base. It can undergo self-ionization and supports hydrolysis reactions.
\( 2H_2O \rightleftharpoons H_3O^+ + OH^- \)
This equilibrium represents the amphoteric nature of water. Water can also act as an oxidizing or reducing agent depending on the reactants.
Role of Water in Life and Environment
Water is indispensable for life. It serves as a medium for biochemical reactions, helps transport nutrients and waste in living organisms, and regulates temperature through sweating and transpiration. On a global scale, it maintains the hydrological cycle — the continuous movement of water through evaporation, condensation, precipitation, and runoff.
Key Reactions of Water
Reaction with Metals
Active metals such as sodium and potassium react vigorously with water to form hydroxides and hydrogen gas:
\( 2Na + 2H_2O \rightarrow 2NaOH + H_2 \uparrow \)
Reaction with Non-Metals
Certain non-metals react with water under specific conditions. For example, chlorine reacts with water to form hydrochloric acid and hypochlorous acid:
\( Cl_2 + H_2O \rightleftharpoons HCl + HClO \)
Electrolysis of Water
When an electric current is passed through acidified water, it decomposes into hydrogen and oxygen gases:
\( 2H_2O(l) \xrightarrow{electrolysis} 2H_2(g) + O_2(g) \)