Water

Water+hydrogen bonding

  • A water molecule consists of two H and one O2 atom=covalent bonds
  • Because the O2 takes electrons from H the water molecule forms a triangle shape=unusual distribution of charges= regions of + and - charge=polar molecule
  • O2 has slight - charge and H has slight + charge=overall neutral charge
  • Water molecules are attracted to one and other by hydrogen bonds
  • Because water molecules are attracted to one and other=flow as a liquid+attracted to charged particles and surfaces

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Unique properties of water

Thermal properties:

  • H bonds between molecules constantly form and break=allows water to flow
  • Water=liquid between 0 and 100 degrees=perfect habitat for living organisms.
  • Acts as an effective coolant due to have high heat capacity=absorbs great amount of heat relative to its mass
  • Water molecules lose kenetic energy as they cool+hydrogen bonds do not break easily=ice is formed
  • At 0 degrees ice is less dense that water so it floats=insulating layer=constant temp under ice=good habitat for organisms

Water as a solvent:

  • Water molecules surround solute molecules and keep them in solution
  • Dissolved solute reacts more easily in metabolic processes
  • Because water is polar=only polar molecules can dissolve in water= carbon cotaining molecules with charged ions= carboxyl groups or amino groups=easily form H bonds.
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Role of water in living organisms

  • Thermostable+solvent ability=water can provide vital role in the body
  •  Water is an ideal transport medium=dissolves polar molecules and ions=transported easily round the body
  • H bonds pull water molecules together so they stick=cohesion
  • H bonds pull water molecules inwards at the surface=tension
  • Insects use the surface tension of the water to skate across the surface
  • Cohesion also allows water molecules to flow in a column
  • Water also adheres to surfaces (adhesion)
  • due to adhesion and cohesion water can travel up narrow tubes, e.g. xylem
  • Non-polar substances cannot dissolve=repelled by water=hydrophobic=important property of phospholipid bilayer of cell membrane
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