KEY POINTS:
- The basic idea of the atom being the smallest part of a substance was accepted for thousands of years – until some great minds decided to look in details at the different elements then known.
- The concept of different atoms having different mass was put forward by John Dalton in the early 1800s.
- J. J. Thomson (1897) then put forward the idea that atoms consisted of negative electrons embedded in a sea of positive charge.
- Ernest Rutherford (1911) then refined this idea further by discovering that the positive charge is actually located within a central nucleus. The positive charges were referred to as protons.
- Neils Bohr (1922) built on this idea and discovered that the electrons were actually orbiting the nucleus in well-defined energy levels (shells).
- James Chadwick discovered the neutrons that exists in the nucleus along with the protons, despite them having no charge and therefore difficult to locate.
- This takes us up to only 1932 – there is almost ninety years worth of further atomic theory that has developed since then.
THINK OUTSIDE THE BOX:
- Do you think scientific knowledge is expanding at an exponential rate? Will we eventually understand the origins of the universe?
- Rutherford can be found on a New Zealand $100 bank note. Are there any other scientists to be found on currency?