Water

• How hydrogen bonding occurs between water molecules

  • Water is a polar molecule (oxygen molecule has a partial negative charge; hydrogen atoms have a partial positive charge)

  • Slightly negatively charged oxygen atoms attract slightly positively charged hydrogen atoms of other water molecules

  • So hydrogen bonds (weak attractive force) form between water molecules
• Properties of water

  - High specific heat capacity

  - high latent heat of evaporation

  - Cohesive

  - Solvent

  - Metabolite
• Properties of water: High specific heat capacity

  Explanation:

  - Polar so many H bonds form between water molecules

  - These allow water to absorb a relatively large amount of heat energy before its temperature changes

  Importance:

  - Good habitat for aquatic organisms

  - Organisms mostly made of water so helps maintain a constant internal body temperature
• Properties of water: High latent heat of evaporation

  Explanation:

  - Polar so many H bonds from between water molecules

  - These can absorb a lot of energy before breaking, when water evaporates

  Importance:

  - Evaporation of small amount of water is an efficient cooling mechanism

  - Helping organisms maintain a constant body temperature
• Properties of water: Cohesive

  Explanation:

  - Polar so many H bonds form between water molecules

  - So water molecules tend to stick together

  Importance:

  - Column of water doesn't break when pulled up a narrow tube e.g. xylem during transpiration

  - Produces SURFACE TENSION at an air-water surface so invertebrates can walk on water e.g. pond skaters
• Properties of water: Solvent

  Explanation:

  - Polar (has a slightly positive and negative ends)

  - Can separate ionic compounds

  Importance:

  - Acts as a medium for metabolic reactions

  - Acts as a transport medium e.g. xylem to transport nitrates which are needed to make amino acids
• Properties of water: Metabolite

  Explanation:

  - Water is reactive

  Importance:

  - Condensation releases H2O and forms a chemical bond; hydrolysis requires H2O to break a bond