Atomic theory timeline

  • 350

    Aristotle 350BC

    Aristotle 350BC
    He proposed that all matter consisted of four elements including Earth, Air, Water and Fire. There were also four qualities including dryness, hotness, coldness, and moistness.
  • 450

    Democritus 450BC

    Democritus 450BC
    He brought up the idea of atom. He proposed that matter was composed of tiny particles, atoms. They join with other atoms to create more atoms.
  • 500

    Alchemists 500BC

    Alchemists 500BC
    First people to test the theories that had emerged about the existence of atoms and the different elements. Before the age of the Alchemists, the concept of atomic theory was just a bunch of ideas.
  • 500

    Leucippus 500BC

    Leucippus 500BC
    One of the first greeks to develop the theory of the atom, which was formalized and elaborated on by his pupil Democritus
  • Isaac Newton

    Isaac Newton
    Proposed a universe with small solid masses in motion.
  • Benjamin Franklin

    Benjamin Franklin
    He introduced the theory that contained the first clear statement of the law of conservation of electric charge.
  • Antoine Lavoisier

    Antoine Lavoisier
    He was the one to formulate the law of conservation of mass, which states that the total mass in a chemical reaction remains constant.
  • John Dalton

    John Dalton
    He proposed that all matter is made of atoms and they are indivisible and indestructible, all atoms of a given element are identical in mass and properties, compounds are formed by a combination of two or more different kinds of atoms, and a chemical reaction is a rearrangement of atoms.
  • John Dalton

    John Dalton
    His atomic model
  • Joseph Proust

    Joseph Proust
    He published his law of definite proportions in 1794 (accepted in 1812).
  • Michael Faraday

    Michael Faraday
    He suggested that the structure of atoms was related to electricity in someway. He developed laws of electrolysis.
  • J. Plucker

    J. Plucker
    Built the first Cathode Ray Tube
  • Dmitri Mendeleev

    Dmitri Mendeleev
    He created the first formal periodic table of element with the 56 elements that were known during his time.
  • Henri Becquerel

    Henri Becquerel
    He discovered radioactivity and was able to isolate radium and polonium.
  • Joseph John Thomson

    Joseph John Thomson
    He did cathode ray experiment and discovered the negatively charged particle, electron.
  • Ernest rutherford

    Ernest rutherford
    He did gold foil experiment and discovered the center of the atom, nucleus.
  • Marie nd Pierre Curie

    Marie nd Pierre Curie
    By studying the decay process of Uranium and Thorium, she discovered radium and polonium and invented the term ‘radioactivity’.
  • Ritherford

    Gold foil experiment
  • Max Planck

    Max Planck
    He used the idea of quanta (discrete units of energy) to explain hot glowing matter.
  • William Crookes

    William Crookes
    Studied the then new concept of radioactivity. He achieved the separation of uranium from uranium-x. He then observed the gradual decay of the product.
  • Albert Einstein

    Albert Einstein
    Published a paper that proved beyond doubt the existence of atoms using the movement of pollen particles in still water, etc.
  • Hans Geiger

    Hans Geiger
    Produced device that made a noise when hit with alpha particles
  • Robert Millikan

    Robert Millikan
    He did oil drop experiment and determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 grams) of an electron.
  • Milikan

    oil drop experiment
  • Niels Bohr

    Niels Bohr
    He developed the Bohr atomic model, with electrons travelling in orbits around the nucleus, and chemical properties being determined by how many electrons are in the outer orbits. He also integrated the Planck quantum theory, stating that when electrons change orbits, they emit a quantum of discrete energy.
  • Henry Moseley

    Henry Moseley
    discovered a systematic mathematical relationship between the wavelengths of the X-rays produced and the atomic numbers of the metals that were used
  • Louis deBroglie

    Louis deBroglie
    He introduced (as his doctoral thesis) his theory of particle-wave duality. This theory suggests that particles can behave like waves, and that waves can behave like particles.
  • Erwin Schrodinger

    Erwin Schrodinger
    He made the modern accepted model of the atom, with orbitals rather than the shells/energy levels that Bohr described.
  • Werner Heinsenberg

    Werner Heinsenberg
    He introduced the uncertainty principle. A principle which states that the speed and location of an electron cannot be determined simultaneously.
  • James Chadwick

    James Chadwick
    He established that atomic number is determined by the numbers of protons in an atom.
    He also discovered the fourth subatomic particle,the neutron.