The Atom

  • John Dalton – proposed a theory about atoms in 1808.
  • William Crookes – investigated what happens when electricity passed through gases.
  • J.J Thomson – discovered the electron.
  • Robert Millikan – measured the size of the charge on the electron.
  • Ernest Rutherford – worked on radioactivity and lead the discovery of the nucleus.
  • James Chadwick – discovered the neutron.

Arrangement of electrons in the atom

  • Niels Bohr – studied the arrangement of electrons in the atom.
  • Werner Heisenberg – put forward his famous Uncertainty Principle.

Erwin Schrödinger – devised mathematical equations to work out the probability of finding an electron in a atom.

The Periodic Table

  • Robert Boyle – first chemist to properly define the meaning of the term ‘element‘.
  • Humphry Davy – discovered many elements by passing electricity through their compounds.
  • Johann Döbereiner – came up with an idea that elements could be categorised in groups of threes called a triad.
  • John Newlands – arranged elements in groups of eight and summarised his ideas in his Law of Octaves.
  • Dmitri Mendeleev – arranged the elements in order of increasing atomic weight (relative atomic mass). His Periodic Table was quite similar to the modern Periodic Table.
  • Henry Moseley – developed a method of determining the atomic number of an element using x-rays.


  • Henri Becquerel – discovered radioactivity.
  • Pierre and Marie Curie – discovered polonium and radium.