ELEMENTS
Every chemical in the world is made up of elements. Just over one hundred elements have been
discovered. Elements are substances that are made of only one type of atom. You will be familiar
with some elements already. Silver, used in jewellery, aluminium, used in cooking foil, and oxygen in
the air you breathe are all elements.
Every element has its own symbol. Symbol are very useful for representing elements. In most
cases the symbol for an element is the first letter or the first two letters of the element´s name.
In some cases the symbol for an element is based on its Latin name. The Latin word for gold is
aurum and its symbol is Au. In the past, most water pipes in houses were made from lead. The
symbol for lead is Pb, which comes from Latin word plumbum, meaning lead. So you can see how
plumbers originally got their name.
COMPOUNDS
When elements join together, they form more complicated substances called compounds. For
example, the compound sodium chloride can be made by the chemical reaction between two
elements- sodium and chlorine. This reaction is quite spectacular as it produces flashes of yellow
flames. You will probably know that sodium chloride is the chemical name for common salt. It´s
interesting to think that something as harmless as this can be made from a violent reaction
between a metal and a poisonous green gas. Elements, therefore, are the building blocks which join
together to form compounds.
Surprisingly, every one of the millions of compounds that exist can be made from just over one
hundred elements.
NAMING COMPOUNDS
Name of compound
magnesium oxide
silver sulphide
Elements present
magnesium and oxygen
silver and sulphur
Names often give you information. The name
of a compound containing two elements
always ends in the letters –ide.
If a compound contains three elements and one of them is oxygen then its name usually ends in the
letters –ate and –ite.
Name of compound
calcium carbonate
lithium sulphite
Elements present
calcium, carbon, oxygen
lithium, sulphur, oxygen
MIXTURES
Imagine some iron filings stirred together with some sulphur powder in a dish. This would be a
mixture of iron and sulphur. A mixture of elements is different from a compound because in a
mixture the elements are not chemically joined. Because of this it is often quite easy to separate
the elements in a mixture. For example, the iron in the mixture of iron and sulphur can be
separated by attracting the iron to a magnet.
The term mixture is also used when different compounds are mixed together. They too can often
be separated easily. For example, imagine a mixture of salt and grit used for putting on roads in
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winter. This mixture can be separated in two steps. The salt is soluble in water and it dissolves
when water is added. The grit can then be separated from the liquid by filtering. Filtering or
filtration is a technique used to separate a soluble from an insoluble substance.
QUESTIONS
1 a) Give the names of the elements which are present in the following compounds.
b) Give their names in Czech.
hydrogen sulphide, zinc nitrate, potassium chloride, barium nitride, magnesium chlorate, sodium
nitrite
2 What is the most important difference between a compound made from iron and sulphur and a
mixture of iron and sulphur?
3 We live in a world of elements and compounds. We are surrounded by them all the time.
a) Name a gaseous element that is around us all the time.
b) Name a solid element you could find somewhere in your home
c) Liquid elements are rare, but can you name a scientific instrument in which you might find
a liquid metal element?
d) What do you think is the most common liquid compound?
e) Name a compound that is present in the air.
4 Complete the following tables:
Compound
Elements present
potassium iodide
_________nitride
________ _______
________ ________
lithium __________
calcium fluorine
Compound
Elements present
_______ carbonate
lead nitrate
________ _______
iron ________ ________
_______ _______ ________
copper sulphur oxygen
5 The burning of petrol in a car engine is an example of a chemical reaction. Explain how this claim
can be justified by answering the following questions:
a) Is there a change in appearance as the reactants turn into products?
b) Does an energy change take place? If so, what forms of energy are released?
c) Are any new substances formed during the burning process? If there are, can you name any of
them?
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