Atomic Theory

  • 400

    Democritus (BC) (Greece)

     Democritus (BC) (Greece)
    Democritus, from Greece, had a theory of which everything comprised of "atoms". He believed these atoms were physically, not geometrically, indivisible, and so called them "atom". He believed that between atoms lies empty space, that atoms are indestructible; have always been and always will be in motion; that there are an infinite number of atoms, and kinds of atoms, which differ in shape and size.
    Democritus created our basis of Atomic knowledge.
  • Period: 400 to

    Atomic Theory Timeline

  • Isaac Newton (AD) (England)

    Isaac Newton (AD) (England)
    Newton proposed that there is a mechanical universe with small solid masses in motion. He also came up with a description of universal gravity by creating the three laws of motion. He contributed to our understanding of the atom because he laid the base for differential & integral calculus, and came up with the idea that there are forces between atoms and that they affect the chemical properties of matter.He help publicise the importance of atoms.
  • John Dalton (AD) (England)

    John Dalton (AD) (England)
    Dalton proposed that there are spherical solid atoms with measurable properties of mass. His theory also stated that atoms of each element were different from one another; ithat they had different masses which helped lead to his conclusion that each atom has its own characteristic weight. He said that compounds were atoms of different elements put together. This contributed to our understanding of the atom because he helped with the development of the modern Atomic Theory.
  • George Johnstone Stoney (AD) (Ireland)

    George Johnstone Stoney (AD) (Ireland)
    Stoney suggested that a subatomic particle existed, which was a particle of electricity held within the atom, named the electron, which was made up of separate negative partiacles.This helped us understand that within the atom, there are other particles and that atoms have a charge.
    Stoney contributed to our understanding of the atom because he came up with the idea of electrons, which furthered our knowledge.
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  • Joseph John Thomson (AD) (England)

    Joseph John Thomson (AD) (England)
    Thomson futhered our Atomic knowledge by discovering isotopes,and confirming that atoms did indeed contain particles known as electrons. He discovered this by carrying out experiments with a CRT (Cathort Ray Tube) and proposed that the charge to mass ratio of an electron is 1.759 x 108 coulombs/gram. He discovered this through finding that cathode rays could be deflected by an electric field, thus concluding that these rays were made from light negative charges. He confrimed Stoney's hypothesis.
  • Max Planck (AD) (Germany)

    Max Planck (AD) (Germany)
    Plank helped us with Atomic Theory by creating the quantum theory by studying the nature of light and other radiation. He also proposed an explanation of hot glowing matter by using the idea of separate units of energy. This contributed to our understanding of the atom because he showed the movement of electrons.
  • Hantaro Nagaoka (AD) (Japan)

    Hantaro Nagaoka (AD) (Japan)
    Nagaoka developed an early, although incorrect "planetary model" of the atom. This was based around an analogy to the explanation of the stability of Saturn’s rings. It had a huge nucleus, with electrons revolving around the nucleus by electrostatic forces. However, this analogy was wrong although the electrons revolving around the nucleus was correct, and was abandoned in 1908.This model (although incorrect) helped develop the idea of the nucleus of an atom being orbited by electrons.
  • Robert Andrews Millikan (AD) (USA)

    Robert Andrews Millikan (AD) (USA)
    Millikan measured the charge on an electron with his oil-drop apparatus. With his oil-drop experiment, he successfully measured the charge and mass of an electron. He also proved that this quantity was a constant for all electrons and so demonstrated the atomic structure of electricity. This means that we know that all the electrons in every atom has the same charge, and that is how he helped us.
  • Ernest Rutherford (AD) (UK, NZ and Canada)

    Ernest Rutherford (AD) (UK, NZ and Canada)
    Rutherford formulated a model of the atom, which was a very small positively charged nucleus, orbited by electrons. He did so by using alpha particles as atomic bullets and probing the atoms in a piece of thin (0.00006 cm) gold foil. This contributed to our understanding of the atom and atomic theory because he visually showed an atom (the nucleus, protons, neutrons and electrons), which had not been seen before. Sourced from:
  • Henry G.J. Moseley (AD) (England)

    Henry G.J. Moseley (AD) (England)
    Moselely discovered the charge of most nuclei by using X-rays. He also discovered that an element's atomic number and number of protons were equal, leading to the Periodic Table of Elements being arranged by atomic number instead of atomic mass, which helped organise it much better. It meant that all atoms of different elements a have different weights.
  • Niels Bohr (AD) (Denmark)

    Niels Bohr (AD) (Denmark)
    Bohr proposed that electrons had a duel nature just like particles and waves and travelled only in certain orbits. He also said that different electron shells have the capacity to hold different numbers of electrons.This contributed to our understanding of the atom because his atomic model explained the underlying regularities of the periodic table of elements. Sourced from:
  • James Chadwick (AD) (England)

    James Chadwick (AD) (England)
    Chadwick discovered the third sub-atomic partical, He named it the ‘neutron’. Nuetrons help stabilise the protons in the atom’s nucleus, preventing the protons from repelling each other. Neutrons are always in the nucleus of atoms, and are about the same size as protons however, they have no electrical charge. Chadwick helped Atomic Theory by helping us to understand why atoms stay together despite the positive charges of the protons. Source: