Biology: WATER

Revision cards on water:

  • How they are formed
  • The polarity of the molecule
  • Properties
  • How it helps living organisms
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Structure of Water

Water (H2O) is made up of 2 hydrogen's and one oxygen atoms. They are joined together by the shared electrons between the molecule. Because of the shared negative hydrogen electrons towards the oxygen atom, the hydrogens are left with a slight postive charge, and the oxygen is left with a slight negative charge. Thus making water a polar molecule with a slight charge on one side, and a slight charge on the other.

                                      Simple diagram showing how water is formed between hydrogen and oxygen (http://t2.gstatic.com/images?q=tbn:ANd9GcTzAw2z7-6eyNY6j05UXyqUXHb6P_OmtaQyFjfsiQ9u97uM9eZz-da42GQx1Q)

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Hydrogen Bonding

Hydrogen bonding is simply the bonding between a slight postive charge on one molecule to the slight negative charge on a different molecule. This is what happens in water: the slight positive charges on the slight positive hydrogens is attracted to the slight negative charge on the oxygen atom. 

HYDROGEN BONDS ARE WEAK!!

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Properties of Water: High Specific Heat Capacity

Because of the hydrogen bonding, water has a high specific heat capacity, which means that is requires a lot of energy to raise the temperature of 1g of a substance by 1C. When water is heated, it takes a lot of energy to break the hydrogen bonding, so there isn't much energy left to actually raise the temperature (it takes a lot of energy to heat it up.) 

It is good for living organisms because this means that large areas of water are able to maintain a stable environment for organisms to live in. 


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Properties of Water: High Latent Heat of Evaporati

Water only evaporate when the hydrogen bonds that hold the water together are broken, thus allowing water on the surface to evaporate as a gas. Because hydrogen bonds require a lot of energy to be broken, this means that it needs a lot of energy to make water evaporate.

It is good for living organisms because they are able to cool down by using evaporation, either by sweating or panting.


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Properties of Water: Very Cohesive

Cohesion is just the attraction between molecules of the same type. Water molecules are very cohesive because they are polar, so they stick together fairly easily. 

It is useful for living organisms because it is able to act as a transport medium for substances, e.g. xylem in the plants transporting water.

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Properties of Water: Lower Density as Ice

When water freezes, it forms ice. Ice is known to be less dense than water, which means that ice will float on top of the water. It produces a surface and an insulating layer between the water and the land. 

It is useful for living organisms because it makes it possible so that animals don't get frozen with the water and they can still live in the water, and it also makes it possible for animals living in the artic to have land to live on.

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Properties of Water: Good Solvent

Because of waters polarity, the slightly positive charged end of the molecule is attracted to the negative charged end of an ion, and the slightly negative charged end of the molecule is attracted to the postive charged end of an ion. Thus meaning that the ion is totally surrounded by water molecules and so it will dissolve.

It helps living organisms because it means that they are able to dissolve useful substances that they need to live, and they can be transported around the body.

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