Timeline of the Atom

  • 350

    Basic concept of atom introduced

    These information was actually introduced by Democritus c.350BC
    - developed a theory which outlined that the universe was made of empty space, and an almost infinite number of indivisible, tiny particles, called atoms.
    - Showing these atoms were different in form, position and arrangement.
    - Describe how natural phenomena's occurred because of the interaction and/or movement of atoms.

    - Formed the beginning of the atom and his theory set up the research and discoveries that would follow.
  • Period: 350 to

    Discovery of the atom throughout time

  • The relation of gravitational force and structure of atom

    Isaac Newton introduced the laws on gravitation (every object in the universe attracts every other object with a force, gravitational force)
  • Atoms forming Elements

    • stating each element was a unique substance and all the atoms forming a particular element were similar and identical in weight. Dalton in 1803
    • stating that all matter is made of minute particles called atoms-atoms cannot be broken down into smaller particles-atoms of the same element are alike-atoms join together in different atoms
    • suggested a simple rule: if two elements form one compound, assume the compound has only one atom
  • Electrons introduced

    G.J. Stoney in 1894
    - introduced the electron as the fundamental unit of electricity.
    - stated that the electron was a twentieth (1o-20) of a quantity of electricity otherwise known as an ampere.
    - introduced the term 'electron' in 1891 but introduced the concept as early as 1874.
  • Proving atoms have no charge

    J.J. Thompson in 1897
    - proposed that atoms were divisible and consisted of electrons.
    - show that atoms had no charge thus the conclusion that atoms were made of negatively charged particles would be incorrect.
    - proposed that the electrons were distributed throughout a sea of positively charged particles like plums were distributed throughout a plum pudding
  • Quantum theory, revolutionizing our study of the atom.

    Planck in 1900
    - explained the glowing of hot matter with quanta
    - explained small discrete units of energy being radiated from the matter.
  • Period: to


  • Simple layout of atom introduced

    Nagaoka in 1903
    - developed an analogy for the layout of an atom.
    - proposed the Saturnian Model which showed that the movement of electrons around the positively charged nucleus was due to a huge nucleus - Saturn's rings are stable because they are orbiting such a massive planet.
    - Proved that electrons moving around the nucleus were bound by electrostatic forces- like gravitational pull keeping the rings of Saturn revolving.
  • Proving that the Knowledge of its charge meant knowledge of its mass.

    Millikan in 1909
    - conducted an oil drop experiment many times and found the charge of the electron to be 1.592 × 10−19 coulomb. His answer is lower than the modern value probably because he measured air viscosity wrong,

    - he found that :a. Charge is quantisedb. The Electron is a sub atomic particle
  • Proved that nucleus is very small but make up most of the weight of the atom.

    E. Rutherford in 1911
    - made a model of the subatomic particles in 1911. In this model there was a central charge surrounding by orbiting particles.
    - His model portrayed the nucleus as very small, but he said it made up most of the weight of the atom. This analogous to the solar system.
  • Describes in details the relationships of activities and interactions in an atom.

    H.G.J Moseley in 1914 introduced law that outlines that the ''square root of the frequencies of lines in atomic x-ray spectra depends linearly on the atomic number of the emitting atom.''
  • Clear layout of the structure of an atom - its shells and electrons

    Bohr in 1922
    - introduced 'shells' in atoms.
    - produced this as a reason why electrons are stable in an atom.
  • the mass relationship of the neutron and protons in an atom

    James Chadswick in 1932 proved the existence of the neutron- it's mass was 0.1% more than the proton's and it had a neutral charge.