Inorganic compounds are
compounds that don’t contain
C and H together. Inorganic
compounds that are important
for living organisms include
water, oxygen, carbon dioxide,
nitrogen and minerals.
• In most living organisms, oxygen is needed to
release energy from food molecules. Organisms
can get oxygen from breathing air or from water.
• Organisms find it more difficult to get oxygen
from water so they tend to be small, flat and
relatively inactive or they are highly adapted with
organs like gills to aid extraction.
• Carbon is an extremely important part of all
living things and needs to be cycled through
ecosystems. Carbon dioxide is the main source
of carbon for the production of the organic
molecules from which living organisms are built.
• Mineral salts are naturally, occurring inorganic
compounds produced by the weathering of
rocks. Important minerals required by
organisms include phosphorus, potassium
calcium, magnesium, iron, sodium, iodine and
sulphur. Others are required in trace amounts.
Plants absorb minerals through their roots,
making them available to be eaten by animals.
• Water is the most abundant compound in our
bodies. Water is the predominant solvent in
living organisms ( this means that things can
dissolve in it), it has a high heat capacity and it
is highly cohesive. This is all due to its structure.
Structure of water
• Each water molecule consists of a combination
of a single oxygen atom with two hydrogen
atoms. Each hydrogen atom is linked to the
oxygen atom by a strong covalent bond
(created by atoms sharing electrons).
• Although water has an overall neutral charge,
the oxygen at the end of a covalent bond is
slightly negative and the hydrogen atoms are
slightly positive areas
• Individual molecules of water are highly attracted
to each other such that the negative oxygen of
one molecule of water is attracted to the positive
hydrogen of another water molecule. These
bonds that hold them together are called
hydrogen bonds which are weaker than
covalent bonds. This means that the hydrogen
bonds that hold them together are relatively
weak and are continually breaking and rejoining.
As a solvent
• Water is the predominant solvent in living
organisms. Its versatility as a solvent is due to
the cohesive nature of the molecule.
• Substances that dissolve readily in water are
called hydrophilic or polar.
• Substances that tend to be insoluble in water are
called hydrophobic or non-polar.
• How do substances dissolve in water?
As a solvent
• Most liquids contract (get smaller) when they get
colder. Water is different. Water contracts until it
reaches 4 C then it expands until it is solid. Solid
water is less dense that liquid water because of
this. If water worked like other liquids, then there
would be no such thing as an ice berg, the ice in
your soft drink would sink to the bottom of the
glass, and ponds would freeze from the bottom
• Surface tension is the name we give to the cohesion of
water molecules at the surface of a body of water. Try
this: place a drop of water onto a piece of wax paper.
Look closely at the drop. What shape is it? Why do you
think it is this shape?
• What is happening? Water is not attracted to wax paper
(there is no adhesion between the drop and the wax
paper). Each molecule in the water drop is attracted to
the other water molecules in the drop. This causes the
water to pull itself into a shape with the smallest amount
of surface area, a bead (sphere). All the water molecules
on the surface of the bead are 'holding' each other
together or creating surface tension.
• Surface tension is related to the cohesive properties of water.
Capillary action however, is related to the adhesive properties
of water. You can see capillary action 'in action' by placing a
straw into a glass of water.
• The water 'climbs' up the straw. What is happening is that the
water molecules are attracted to the straw molecules. When
one water molecule moves closer to a the straw molecules the
other water molecules (which are cohesively attracted to that
water molecule) also move up into the straw. Capillary action
is limited by gravity and the size of the straw.
• Plants take advantage of capillary action to pull water from the
soil into themselves. From the roots water is drawn through
the plant by another force, transpiration.
Water resists changes in
• Hydrogen bonding is the cause, like for so many of
water's properties, for it's high specific heat capacity.
Heat is released when hydrogen bonds form and heat
must be absorbed in order to break hydrogen bonds.
• A calorie of heat causes a rather tiny change in the
temperature because most of the heat energy is used to
disrupt hydrogen bonds before the molecules can begin
moving faster. As the temperature of water drops, many
additional hydrogen bonds form at the same time. This
releases a substantial amount of energy in the form of
Summary of properties
Properties Chemical Reason Effect
Resists changes in
Hydrogen bonding Helps keep body
Universal solvent Polarity Facilitate chemical
Is cohesive and
Serves as a transport
Has a high surface
Hydrogen bonding Difficult to break
Less dense as ice than
as liquid water
Hydrogen bonding Ice floats on water