Water

• 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

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.

• 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