Development of the atom

• Solid sphere model (John Dalton, 1803)


  All matter was made up of tiny spheres that couldn't be broken down into anything smaller
• Plum pudding model (J.J Thomson, 1904)

  Atoms contain tiny particles called electrons, they were embedded in a ball of positive charge
• Discoveries in the plum pudding model


  Scientists did experiments which discovered electrons.
• What was the first subatomic particle to be discovered in the plum pudding model?

  Electrons- tiny, negatively charged particles
• Nuclear Model (Ernest Rutherford 1911)


  Atoms had a small, central positive nucleus, and electrons floated around
• Neils Bohr (1913) Bohr Model

  Atoms had a small, central nucleus which was positive and electrons orbit the nucleus at fixed distances and these orbits are called shells or energy levels
• James Chadwick (1932) Current Model/Quantum Model

  Atoms have a small central nucleus containing protons and neutrons with electrons orbiting around it in shells
• What did James Chadwick discover in the atomic model?

  The nucleus contained particles with no charged- called neutrons.
• What are the key differences between the nuclear model and the plum pudding model of atoms?


  • Nuclear model is mostly empty space; plum pudding model has no empty space
  • Plum pudding model is solid
  • Positive charge is in the nucleus in the nuclear model; in the plum pudding model, it is a ball of positive charge
  • Mass is concentrated in the nucleus in the nuclear model; in the plum pudding model, mass is spread out
  • Electrons and nucleus are separate in the nuclear model; in the plum pudding model, electrons are embedded
• Discovery of the proton (1920)

  Later experiments found that the positive charge of any nucleus can be subdivided into a whole number of smaller particles of equal charge, these were named protons
• Discovery of the neutron (1932)

  James Chadwick discovered neutrons