Atomic Theory Timeline

  • Jan 1, 1001


    Greece Atoms are indestructible, eternal, and are in constant motion. They are not all the same as they differ in shape and position. When the atoms move they come into contact with other atoms and form bodies. A thing comes into being when the atoms that make it up are appropriately associated and passes away when these parts disperse.
  • Issac Newton

    England Heat is a molecular motion, and how such heat is generated when dissimilar molecules that attract each other are mixed, so their potential energy translated into kinetic energy as they move towards each other.
  • John Dalton

    England All matter consists of tiny particles, atoms are indestructible and unchangeable, elements are characterised by mass of their atoms and when elements react, their atoms combine in simple, whole-number ratios
  • George Johnstone Stoney

    Ireland He introduced the term ‘electron’ into science. He made a crucial distinction between two types of molecular motion.
  • Joseph John Thomson

    Briton He discovered that electrons and protons are subatomic particles. He also stated that electrons were positioned by electrostatic forces.
  • Max Planck

    Germany He discovered the law of heat radiation, which is now named Planck’s law of black body radiation.
  • Hantaro Nagaoka

    Japan Postulated a ‘Saturnian’ model of the atom with flat rings of electrons revolving around a positively charged particle.
  • Robert Andrews Millikan

    America He discovered that the weight of an electron is 1836 times smaller than a hydrogen atom.
  • Ernest Rutherford

    United Kingdom
    He established that the nucleus was very dense, very small and positively charged.
    He built a model called ‘Solar system model’ which was of the atom with a nucleus orbited by electrons.
  • Henry Gwyn-Jeffreys Moseley

    Briton He found that atoms of each element contain a unique positive charge in their nucleus. This discovery helped to solve the mystery of what makes the atoms of one element different from those another; an atom’s identity comes from the number of protons in it nucleus.
  • Niels Bohr

    Denmark He developed an explanation of atomic structure that underlies regularities of the periodic table of elements.
  • James Chadwick

    England He discovered that the neutron did exist and its mass is about 0.1 percent more than the proton.