Properties of Water

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Properties of Water

Water has unique properties that make it essential for life. These properties result from hydrogen bonding between water molecules, giving water its cohesive, adhesive, and thermal properties.

Hydrogen Bonds in Water

  • Polar Covalent Bond: Within a water molecule (H₂O), the oxygen atom shares electrons with hydrogen atoms, creating a polar covalent bond. Due to oxygen’s higher electronegativity, it pulls the electrons closer, giving oxygen a partial negative charge (δ⁻) and hydrogen atoms a partial positive charge (δ⁺).
  • Hydrogen Bond: This polarity allows water molecules to form hydrogen bonds, where the partially positive hydrogen of one molecule is attracted to the partially negative oxygen of another. These hydrogen bonds are weaker than covalent bonds but are strong enough to create a “web” or network of interactions.

1. Cohesion

  • Definition: Cohesion is the attraction between molecules of the same substance.
  • In Water: Water molecules stick together due to hydrogen bonds, creating cohesive forces.
  • Examples:
    • Water droplets on wax paper form close-together beads, demonstrating cohesion.
    • Rain droplets combine on a window due to cohesive forces.
    • Water forms a dome on a penny because the molecules stick together.

2. Adhesion

  • Definition: Adhesion is the attraction between molecules of different substances.
  • In Water: Water can stick to other surfaces, like glass, metal, or paper, due to adhesive forces.
  • Examples:
    • Water sticks to aluminum foil, forming a pile rather than spreading smoothly.
    • Water adheres to a paper surface or moves up a straw (capillary action).
    • Water droplets on a penny cling to its surface.

3. Surface Tension

  • Definition: Surface tension is the "film" or "web" formed on the surface of water due to cohesive forces.
  • In Water: Hydrogen bonds between water molecules create a surface that resists external force.
  • Examples:
    • A penny can hold a surprising number of water droplets because of water's surface tension.
    • Small insects like water striders can walk on water due to surface tension.

4. Heat Capacity

  • Definition: Heat capacity is the amount of heat required to change a substance's temperature.
  • In Water: Water has a high heat capacity, meaning it can absorb a large amount of heat with minimal temperature change.
  • Example: Swimming pools remain cool even in hot weather because water absorbs heat without significant temperature increase.
  • Reason: Water’s high heat capacity is due to hydrogen bonds, which require energy to break, allowing water to absorb heat without rapid temperature changes.

Water’s cohesion, adhesion, surface tension, and heat capacity are essential for various biological processes, such as nutrient transport in plants, temperature regulation, and maintaining habitat stability. These properties make water a unique and vital component of life on Earth.

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