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1. Inside atoms and elements page 2
Periodic table
Picture 1.2 The elements are arranged in the Periodic Table. In 2001, there were 115 known elements. Click here to see the full table.
Elementary, my dear
In the eighteenth century, chemists began finding elements – substances that could not be made any simpler using chemical reactions. One chemist, John Dalton, suggested that these elements were made up of atoms and that the atoms of an element are all the same. This simple model could explain the millions of different materials around us.

The elements
There are more than 109 different types of atom - one for each element. Differences between the atoms give the elements their different chemical properties.

In 2001, there were 115 known elements. However, those above 109 are highly unstable and have been made in only tiny quantities.

Scientists are able to make tiny amounts amounts of these new elements in the laboratory. They exist for only a very short time so, whilst they are of scientific interest, they have little practical use in the wider world – at the moment!

The tiniest particle?
When enough atoms combine together we begin to get matter that we can see. This full stop is made from about 10 million million atoms in the phosphor of your computer screen.

Atoms and molecules interactive graphic
Picture 1.3 Atoms are tiny. Only when lots of them join together can we see visible lumps of elements or compounds.

Elements and compunds
Atoms can combine with atoms of the same element (for example, oxygen, hydrogen or a lump of carbon). Or they can make compounds by combining with atoms of different elements (for example water or carbon dioxide).

The number of different combinations of atoms (making compounds) is vast. From only about 100 elements we get the millions of different materials we see around us every day.

Question 1
a) Imagine apples, oranges and pears to be atoms of three different elements. How many different combinations of two atoms can we make?
(Type a number in the box).
b) i. How many of these combinations are still elements?
(Type a number in the box).
b) ii. What would we call combinations of two different atoms?
c) Look at these substances. Which ones are elements and which are compounds?
  i. water
  ii. oxygen
  iii. hydrogen
  iv. carbon dioxide
  v. iron
Note: Although we often draw atoms as coloured balls, this not what they really look like. In fact, they are too small to see directly because they are smaller than light waves. So it is meaningless to think of them having any colour.
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