Element A substance that cannot be broken down into simpler substances by chemical means.
Atom The smallest part of an element.
Sub-atomic
particles Particles that atoms are made of.
The ink on this page is made from the element carbon. The full stop at the end of this sentence has approximately 75,000,000,000,000 (75 trillion) particles of carbon in it. We call these particles atoms. An atom is the smallest part of an element. A single atom of carbon is the same as every other atom that makes up a piece of carbon containing trillions of carbon atoms. Each carbon atom is made of even smaller sub-atomic particles. The sub-atomic particles make up the carbon atom but on their own they do not have the same properties as a carbon atom.
22.2 Structure of an atom
Atoms, although they are extremely tiny, are actually mostly made up of empty space. They have a dense nucleus in their centre where almost all the matter is held. If an atom was the size of the Aviva Stadium, then the nucleus would be the size of a marble in the centre of the pitch.
Marble
Fig. 2 The size of the nucleus in an atom can be compared to a marble in the centre of the Aviva Stadium. Research this
Find out who discovered that the atom has a nucleus and how it was discovered.
Protons, electrons and neutrons Atoms are made up of three types of sub-atomic particles. These are called protons, electrons and neutrons. Each of these sub-atomic particles has different properties:
