Biology AS level OCR f212.

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  • 2 hydrogen atoms covalently bonded to oxygen atom
  • oxygen is more electronegative than hydrogen
  • unshared electrons give oxygen atom a slight negative charge and each hydrogen atom a slightly positive charge.
  • makes water a POLAR MOLECULE 
  • negatively charged oxygen atoms of 1 water molecule attracts positively charged hydrogen atom of another water molecule
  • this attraction is called HYDROGEN BONDING.
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PROPERTIES OF WATER caused by hydrogen bonding

  • HIGH SPECIFIC HEAT CAPACITY- amount of energy needed to raise the temperature of a 1kg substance by 1degree celsius.
  • hydrogen bonds can absorb a lot of energy so a lot of energy is needed to heat it up.
  • useful for organisms- it stops the rapid temperature change and keeps body temp fairly stable even as external environment heats up.
  • HIGH LATENT HEAT OF EVAPORATION-amount of energy absorbed by a substance without raising its temp as it changes from one state to another.
  • a lot of energy is needed to break  hydrogen bonds between water molecules.
  • useful- helps in cooling when we sweat(water in sweat absorbs heat from body as it evaporates). also cools plant leaves in hot climates as water evaporates from mesophyll cells.
  • POLARITY makes water very COHESIVE(attraction between molecules of same type).
  • useful- helps water to flow in mass,great for transporting substances.
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  • polarity makes it a good solvent for polar substances.
  • negative oxygen attracted to postive molecule and positive hydrogens attracted to negative molecule. 
  • causes substances to dissolve- separation and dispersal of molecules or ions of a substance between the molecules of the solvent.
  • SURFACE TENSION- uppermost water molecules are pulled downwards.pulling forces draw them closer together. this forms strong layer on surface of the water.
  • small animals are able to walk on it without difficulty.
  • water is relatively dense(1.0g/cm3)-caused by molecules being pulled closely together by hydrogen bonds.
  • water is fairly viscous
  • Aquatic animals are streamlined,have cartilagous bones and air bladders to help them cut through water molecules more easily.
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