2.1.1 AS BIOLOGY OCR

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  • Created by: Maryan
  • Created on: 29-02-12 21:27

Hydrogen Bonding

  • A water molecule occurs when one O atom is joined to 2 H atoms - H20 through sharing of electrons.
  • The shared H atoms are pulled towards the Oxygen atom and the other side of the H atoms are left with a slight + charge.
  • The oxygen atom has unpaired electrons so it has a slight negative charge.
  • These charges make water polar:
  • The - on the O and the + on the H

How this forms the structure:

The  - charged O atoms attract other water molecules through the + charged H atoms: this is called Hydrogen Bonding.

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How this forms the structure:

How this forms the structure:

The  - charged O atoms attract other water molecules through the + charged H atoms: this is called Hydrogen Bonding.

(http://t3.gstatic.com/images?q=tbn:ANd9GcSK13it2WjTLP4umubkjTTowDkE86GmfV1ffZwZu4FtXEFToVsb)(http://t3.gstatic.com/images?q=tbn:ANd9GcTNBOBA71wG6q1lE3f_JlrzNtwaoIlCxfQi8kQ4HV15DOQXBn0pUg)

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Roles in lving organisms

  • Reactant:
  • Reactant in lots of important chemical reactions e.g. photosynthesis and hydrolysis reactions
  • Universal solvent:
  • Its a solvent to many substances and this is important because most reactions take place in solutions
  • Transport substances:
  • Its a liquid and a solvent so can transport many different things e.g. glucose and oxygen around animals
  • Temp control
  • Helps water maintain a certain temperature by evaportating the surface of the water when it gets too high , this cools it down. Useful for living organisms who live in the sea
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Properties

High specific heat capacity:

  • The H bonds between water molecules can absorb a lot of heat energy
  • So it takes a lot of energy to break water molecules
  • Useful for living organisms because it maintains a certain temperature by stopping rapid temp changes

Hig latent heat of evaporation

  • Evaporation of water cools surfaces by providing the heat neccesary for evaporation.
  •  takes a lot of heat energy to break H bonds in the first place
  • Useful for liiving organisms because they can resist body temp changes ( as their bodies contains lots of water)
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Properties

Cohesion:

  • A water molecule will attract neighbouring water molecules so they tend to stick together
  • This happens because they are polar
  • helps water to flow- good for transporting substances e.g. in xylem via the transpiration stream

Surface tension:

  • Caused by cohesion
  • Water molecules at the surface are attracted to those below and adjacent
  • Reduces the surface to the smallest possible area
  • acts like a extremely think membrane
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