Atomic Timeline

By Tom037
  • 400 BCE

    The Idea of an Atom was Suggested

    Democritus suggested evrything was com[osed of invisible particles. Suggested: atoms are industructible, the number of atoms is infinite, and toms could differ in size, shape, and weight.
    Democritus proved the existence of an atom by splitting a piece of gold in two and showing theat they both retained their properties. However this did not explain the structure of the atom.

  • The Theory of Elements was Proven

    John Dalon conducted an experiement that proved all elements are composed on small atoms.
    Dalton Theorised the law of constant composition, the number of atoms is constant. THe law of conservation of mass, matter cannot be destroyed or created. The law of multiple proportions.

  • Sub-Atomic Particles were Discovered

    JJ Thompson discovered atoms were divisble and were comprised of sub-atomic particles. Proposed the 'Plum Pudding Model'. Belived atoms were nuetrally charged.
    Supported by experiments using cathode ray tubes. However could not explain Rutherfords' scattering experiment.

  • It was Discovered that atoms are mostly empty space

    Ernest Rutherford disporved the Plum Pudding model with his gold foil experiment and determined that atoms are mostly empty space with a positive centre and surrounded by diffuse negative charges.
    By scattering particles it showed that they had a dense nucleus. However other data recorded was not valid. Also it could not explain atomic spectra.

  • The Bohr Model

    Niels Bohr improved the Rutherforb Model by suggesting that electrons orbit the nucleus at specific energy levels. Can only change energy level by absobing and releasing energy.
    The Bohr model was able to explain the atomic spectra of hydrogen however not other elements. It also introduced the concept of shells and energy levels.

  • Quantum Mechanics and Orbitals

    Louis de Broglie, Erwin Schroginger, & Werner Heisen Berg contributed to the quantum mechanical model it proposed: sub-atomic particles has wave nature, the concept of orbitals and measuring electrons.
    An orbital is a region of space which there is a high probability of finding a certain atom. May be severeal orbitals with different shapes and energy levels. Orbital model is supported.

  • The Neutron was Discovered

    James Chadwick discoved the existence of an electronically charged sub-atomic particle called a neutron.
    Chadwick produced a new kind of radiation and is composed on a neutral electrical charge with the approximate mass of a proton.