The metal elements in the periodic table have easily
defined properties. The remaining elements, however, have very different
properties. They consist of a group of unreactive gases called the NOBLE GASES, a group of reactive elements known as the HALOGENS,
and a set of elements referred to as non-metals. In addition, a few elements
have properties that place them in between metals and non-metals. They are
called the SEMI-METALS.
Deposits of the non-metal sulphur are found as deep as 300 m (1,000
ft) below ground. Combined with other elements, sulphur is also found in rocks
and minerals, such as gypsum.
Sulphur crystals are ground to a powder at sulphur processing
plants. The powder is sprayed into a furnace where it reacts with oxygen,
forming sulphur dioxide. More oxygen is reacted with the sulphur dioxide to
make sulphur trioxide, which is dissolved in water to make oleum.
TRANSPORTING SULPHURIC ACID
Oleum is concentrated sulphuric acid. It is transported to
manufacturing plants in tankers. Here, water is added to the oleum in precise
measures to make the correct concentration of sulphuric acid. Sulphuric acid is
used in the manufacture of detergents, paints, medicines, plastics, and
synthetic fabrics.
The elements known as semi-metals have some of the
properties of metals and some of the properties of non-metals. Arsenic, for
example, has the shininess of a metal but does not conduct heat or electricity
very well. Other semi-metals, such as silicon and germanium, are
semi-conductors. This means that they can conduct electricity, but only under
special conditions. This property makes them very useful in solar panels and
computers.
At first sight, the halogens don’t seem very
alike. For example, fluorine is a yellow gas and iodine is a shiny, black
solid. However, they are all highly reactive and are quick to combine with
other elements to form salts, such as table salt (sodium chloride). They also
have important uses. Chlorine is used to disinfect water, and compounds of
fluorine – fluorides – are added to toothpaste to prevent tooth
decay.
In X-ray photography, a plastic film is coated with a paste of a
bromine compound called silver bromide. When X-ray light strikes the film, the
silver bromide breaks apart and pure silver atoms are left on the film. The
more intense the light, the more silver atoms are formed and the darker that
part of the image becomes.
Group 18 of the periodic table contains the noble gases.
These six unreactive gases do not combine with other elements, so they are
usually found on their own. Nearly 1 per cent of air is argon. Traces of neon,
helium, krypton, radon, and xenon are also found in air. Argon is used in light
bulbs, xenon is used in lighthouse arc lamps, and helium is used to fill
airships and hot-air balloons.
A neon light is a tube containing a noble gas, but not always
neon. When electricity is passed through the tube, the atoms of the noble gas
emit (give out) light of different colours. Helium emits a yellow light, neon a
red light, argon a blue light, and krypton a purple light. Other colours are
created by giving the glass tube different coloured coatings.
