Lecture Notes: Unique Properties of Water

Introduction

• Water is a polar molecule shaped like an outstretched 'V'.
• Comprises ¾ of Earth's surface.
• Essential for life; unique properties important for biology.

Molecular Structure and Polarity

• Water's polarity:
  • Oxygen is very electronegative, keeps electrons closer.
  • Oxygen has a slightly negative charge; hydrogens have a slightly positive charge.
• Hydrogen bonds form between water molecules.

Unique Properties and Biological Significance

1. Cohesion and Adhesion

• Cohesion: Water molecules stick to each other.
  • Contributes to surface tension.
  • Allows for phenomena like water striders skating on water.
• Adhesion: Water sticks to other surfaces.
  • Helps in the movement of water through plant xylem against gravity.

2. Solvent Properties

• Water dissolves many substances, especially polar molecules and ionic compounds.
• Essential for biological processes, such as kidney filtration and bodily fluids.

3. Density and Ice Formation

• Water expands when it freezes, becoming less dense.
• Ice forms an insulating layer:
  • Important for aquatic life to survive under ice.
  • Due to hydrogen bond lattice structure in ice.

4. Specific Heat Capacity

• Water has high specific heat:
  • Resists temperature changes.
  • Stabilizes aquatic environments and moderates climate.
• Absorbs heat in summer, releases heat in winter.

5. Evaporative Cooling

• Evaporation used by animals to cool down:
  • Faster, higher energy water molecules escape as gas.
  • Loss of heat from the skin.
• Plants also use evaporative cooling to prevent damage from excessive heat.

Conclusion

• Water's unique properties are crucial for the survival and functioning of living organisms.
• Encouraged to appreciate the significance of water in everyday encounters.