water Flashcards
What does the word ‘polar’ mean?
A separation of charge
A molecule with a slightly negative charge on one side and a
slightly positive charge on the other
Water is a polar molecule
Structure of water
One atom of oxygen joined to two atoms of
hydrogen by a covalent bond – shared
electrons
Hydrogen’s shared electrons are pulled
towards the oxygen atom, causing each
hydrogen atom to be left with a slightly
positive charge
Oxygen has the greatest share of the
electrons making it slightly negative in
charge.
This makes water a polar molecule: a
dipole
Hydrogen bonding in water
slightly negative charge on the oxygen atom is attracted to and forms a hydrogen bond with the slightly positive hydrogen atom of another water molecule.
The properties of water
High specific heat capacity
High latent heat of
vaporisation
Very cohesive
Lower density when solid
Good solvent
High specific heat
capacity of water
Hydrogen bonds between water molecules
can absorb a lot of energy.
Water has a high specific heat capacity meaning a lot of energy is required to
raise the temperature.
Large fluctuations in temperature do not occur, which provides a stable,
constant environment for aquatic organisms.
High Latent Heat of
Vaporisation
A lot of energy is needed to break the hydrogen bonds between water molecules to change water to a gaseous
state.
This makes water an excellent coolant.
Mammals sweat, which evaporates, carrying heat away
Plants – transpiration – water evaporates from leaves, carrying heat away
Temperature buffer for chemical reactions occurring in prokaryotes and eukaryotes
Proper function of enzymes - active in a narrow temperature range.
Cohesion
the attraction between water molecules due to hydrogen bonding.
Transport
Transpiration – water molecules hydrogen bond to each other, stick together and are drawn up xylem tubes
Blood
Phloem
Surface tension – provides habitat
Surface Tension
Water molecules are more attracted to each other than they are to air molecules.
The water has a ‘skin’ of surface
tension which can provide a habitat
Adhesion
is the attraction between a water molecule and another polar molecule
due to hydrogen bonding.
The water droplets ‘stick’ to the leaf due to
adhesion.
The combination of adhesion and cohesion of water is capillary action.
This is what allows water to move through the xylem tubes.
Lower density when
solid
As water changes state from liquid to solid, each water molecule forms four hydrogen bonds to other water molecules, creating a hexagonal lattice shape. This makes ice less dense than liquid water.
Which is why ice floats.
Ice forms a protective layer which reduces
the rate of heat loss and makes the environment more stable for aquatic
organisms.
good solvent
Water molecules surround each ion, and in this way they dissolve.
Water is polar therefore the slightly positive end of a water molecule will be attracted to negative ions. The slightly negative end will be attracted to positive ions.
Ionic bonds form between the water
molecules and the potassium/chloride
ions.
Transporting molecules and ions in living
organisms (blood / phloem).
Ions can dissolve in water in blood and are
important in the regulation of pH and water
balance.
Most chemical reactions take place in a
solution.
Which substances dissolve in water?
Ions and other polar substances
To identify these, look for the –OH groups and –SH groups in chemical structures:
Why is it useful to organisms that water is a liquid at room temperature?
Effective transport medium e.g.,
blood/phloem
Habitat for aquatic organisms
Medium for chemical reactions
