Discovery of the Proton & Neutron (AQA GCSE Combined Science: Trilogy: Physics): Revision Note

The Discovery of the Proton

• The nuclear model was improved when the particles within the nucleus were discovered

• Ernest Rutherford discovered that the positively charged nucleus of all materials could be broken down into smaller positively charged particles

• The smallest of these parts had the same charge as a Hydrogen nucleus

  • This amount of charge is called the elementary charge

• He called the positively charged particles in the nucleus as protons

  • ‘Proto’ means original - protons are the original unit of positive charge

The Discovery of the Neutron

• After the discovery of the proton, many scientists saw evidence of another particle in the nucleus but could not prove it

• It was about 20 years after models of the nucleus at the centre of the atom, that the final particle was confirmed

• In 1932, James Chadwick proved the existence of neutrons in the nucleus, he discovered:

  • A neutron has a mass similar to the proton

  • A neutron has no charge - it is neutral

• The discovery of the neutron gave another, better model of the atom

  • A positive, dense nucleus made from neutrons and protons

  • Negative electrons on different energy levels orbit the nucleus

The models of the atom changed a lot at the start of the 20th Century. The discovery of the neutron allowed this model to be created