P6 OCR Science

The nucleus of an atom contains protons and neutrons.

It makes up most of the mass of the atom, but takes up virtually no space - it's tiny.

The electrons are really really small.

They whizz around the outside of the atom.

Their paths take up a lot of space giving the atom an overall size (though it's mostly empty space).

1) Every atom of a particular element has the same number of protons in it's nucleus, e.g. every carbon atom has 6 protons in it's nucleus, every nitrogen proton has 7 protons in it's nucleus, etc.

2) The number of neutrons isn't fixed though. Many elements have a few different isotopes - atoms with the same number of protons but different number of neutrons.

3) E.g. There are two different isotopes of carbon - carbon-14 has two more neutrons than more carbon (carbon-12).

4) Usually each element only has one or two stable isotopes - like carbon-12.

5) The other isotopes tend to be radioactive - the nucleus is unstable so it decays (breaks down) and emits radiation. Carbon-14 is an unstable isotope of carbon.

1) Some elements emit ionsing radiation all the time - these elements are radiocative.

2) Radiocative atoms are unstable - they break up (decay) to make themselves more stable.

3) Unstable atoms decay at random and you can't predict when it will happen - it's completely unaffected by physical conditions (like temperature) or physical processes (e.g. bonding)

4) When an atom does decay it spits out one or more of three types or ionising radiation - alpha beta and gamma.

5) In the process the atom often changes into a new element.

6) Ionising radiation can transfer enough energy to break an atom or molecule into bits called ions - this is called ionisation.

7) These ions can then go on to take part in other chemical reactions