Contents
Elements (i) ........................................................................... 1
Elements (ii)........................................................................... 2
Compounds and mixtures ................................................. 4
Solutions................................................................................. 4
Hazards (i) ............................................................................. 5
Hazards (ii) ............................................................................ 6
Unit 1a
Substances
Elements (i)
Everything in the world is made from about one hundred
elements. Each one has a name and a symbol that consists of
one or two letters. The first letter is always a capital letter (upper
case) and the second letter is always lower case (a small letter),
e.g. the symbol for carbon is C but the symbol for calcium is Ca.
The symbol for some elements is based on the Latin name, e.g.
the symbol for potassium (kalium) is K and the symbol for sodium
(natrium) is Na.
Chemists have arranged
elements in the Periodic Table.
Most elements are solid at room temperature, e.g. carbon and
copper. The two elements that are liquid at room temperature
are bromine and mercury.
Some elements are gases at room temperature, e.g. oxygen and
hydrogen.
Many other examples of solids and gases are acceptable.
Elements can be classified as metals and non-metals.
There are many more metals than non-metals.
The metals are found to the left side of the zig-zag line in the
Periodic Table. Some elements, including gold, silver and
copper have been known for a long time. The most recently
discovered elements have been made by scientists. These
elements are found after uranium at the bottom of the Periodic
Table.
Elements (ii)
Elements in the same group of the Periodic Table show similar
chemical properties, e.g.
sodium, lithium and
potassium are all stored
under oil because they are
very reactive.
Elements are used for many
things.
Some examples of everyday uses of elements are shown in the
table.
Element
Use
Aluminium
Double-glazing frames, etc.
Chlorine
As a disinfectant in swimming pools.
Zinc
Battery cases, etc.
Carbon
As graphite in pencils, etc.
Iron
Nails, etc.
Argon
The gas in light bulbs, etc.
Other uses of the elements are acceptable.
Compounds and mixtures
A compound is a substance that is made up of two or more
elements joined together, e.g.
iron
+
sulphur
iron sulphide
Compounds with a name ending in ‘-ide’ contain the two
elements indicated, e.g. the compound that contains calcium
and oxygen is called calcium oxide.
Similarly, sodium chloride contains sodium and chlorine.
The name ending ‘-ite’ or ‘-ate’ indicates the additional element
oxygen in the compound, e.g. potassium sulphite and potassium
sulphate both contain potassium, sulphur and oxygen.
When two or more substances come together without reacting, a
mixture is formed. Air is a mixture of gases, approximately 80%
nitrogen and 20% oxygen.
The test for oxygen is that it relights a glowing splint.
A glowing splint does not relight in air because there is not
enough oxygen.
Solutions
A solution is formed when a substance dissolves in a liquid.
Copper sulphate
solution
+
water
copper sulphate
A substance that dissolves in a liquid is soluble; a substance which
does not dissolve is insoluble.
A solution is diluted if more liquid is added to it.
A dilute solution has a lower concentration of dissolved substance
than a concentrated solution.
A saturated solution is one in which no more substance can be
dissolved.
The gas which is dissolved in some drinks to make them fizzy is
carbon dioxide. The test for carbon dioxide is that it turns lime
water milky.
The substance that dissolves in the liquid can be a solid, a liquid
or a gas, e.g. sugar is a solid that dissolves in water, alcohol is a
liquid that dissolves in water and sulphur dioxide is a gas that
dissolves in water.
In some places, to kill bacteria, chlorine is
added to our drinking water. To prevent
tooth decay, sodium fluoride is added.
Compounds of lead, which can get into
drinking water from old pipes, can be harmful to health.
Hazards (i)
Regulations on the use of chemicals exist to ensure a safe working
environment for everyone who comes into contact with
chemicals at work.
Simple hazard warning symbols, which can be easily recognised,
are used to identify the potential dangers of all chemicals.
Hazard symbols are on road tankers to
indicate dangers in the event of accidents.
This shows that the chemical is toxic (a poison).
Taking or eating these chemicals would make you
feel very unwell and may even cause death.
This shows that the chemical is corrosive (sometimes
called caustic).
These chemicals can cause severe burns to the skin,
as well as holes in some metal objects.
This shows that the chemical is flammable
(sometimes called inflammable, which is the same
thing).Flammable chemicals catch fire and burn
very easily.
Hazards (ii)
This shows that the chemical is an irritant or harmful
chemical. Chemicals with this warning symbol can
make you feel very unwell by affecting your skin or
organs. In many cases your lungs or breathing
system can be badly damaged by these chemicals.
This shows that the chemical is explosive. As you
might expect chemicals with this warning symbol
can explode!
This shows that the chemical is radioactive.
Exposure to radiation can be harmful and may lead
to cancer. This is why hospital staff in the x-ray
department will wear special (and very heavy)
clothes, or they will stand behind a protective
screen.