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.
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.
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 Elements present
calcium carbonate calcium, carbon, oxygen
lithium sulphite lithium, sulphur, oxygen
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 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: