Inorganic molecules
Inorganic compounds are compounds that don’t contain C, H and O. Inorganic
compounds that are important for living organisms include water, oxygen,
carbon dioxide, nitrogen and minerals.
Oxygen
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 dioxide
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.
Nitrogen
Nitrogen is a component of all proteins and is therefore required by organisms in large
amounts. Nitrogen enters living things via the nitrogen cycle.
Minerals
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
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
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.
Cohesiveness
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. This constant
joining and breaking that water molecules retain their cohesive nature.
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?
Surface tension
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?
Capillary action
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?
Density
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 up!
Water resists changes in temperature
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 heat.
Properties
Resists changes in
temperature
Universal solvent
Is cohesive and adhesive
Has a high surface tension
Less dense as ice than as
liquid water
Chemical Reason
Effect