Timeline of the Atom- Scientists & their ideas.

Timeline created by bahahahahahaha
  • 470

    Democritus proposed that there are atoms and void. (Greece)

    Democritis is a Greek scientist whoose discovery, in 400 BCE, lead him to theorise that everything is made up of void and atoms. Depending on the arrangement, the density varies with less void being denser. His discovery has helped the development of the modern atomic theory. He quoted, "by convention bitter, by convention sweet, but in reality atoms and void."
  • Isaac Newton proposed a mechanical universe with small solid masses in motion. (England)

    Newton recognised that there are forces between atoms and that they affect the chemical properties of matter.He helped publicise that atoms affect the chemical properties of matter and helped us understand that atoms are what make everything work.
    These forces are now understood by Quantum mechanics.
  • John Dalton proposed an "atomic theory" with spherical solid atoms. (England)

    John Dalton was an English scientist who theorised that chemical element atoms have a unique atomic weight and can be placed in order on what is known today as the periodic table of elements.
  • G.J. Stoney proposed that electricity was made up of “electrons ". (Ireland)

    Stoney suggested that a subatomic particle existed which was a particle of electricity held within the atom, named the electron.This helped us understand that within the atom, there are other particles and that atoms have a charge (as electricity is charged).
  • J.J. Thomson concluded that there were small, electrically, negatively charged particles that are 1000 times less that a hydrogen atom. (England)

    Thomson discovered that atoms did indeed contain particles known as electrons. He discovered this through finding that cathode rays could be deflected by an electric field, thus concluding that these rays were composed of very light negatively charged particles which he called ‘corpuscles’, later to be named ‘electrons’.This proved Stoney’s hypothesis (and thus other consequences) was correct.
  • Max Planck used the idea of what he called quanta to explain the radiation from a radiating atom. (Germany)

    Planck discovered quantum theory, by studying the nature of light and other radiation. He hypothesised at very small scales, that matter was discrete rather than continuous.This means that we know that atoms behave differently to the human-scale world that we know and perceive.
  • Hantaro Nagaoka created a model of the atom and explained how atoms kept electrons in orbit. (Japan)

    Nagaoka developed an early, incorrect "planetary model" of the atom which was based around an analogy to the explanation of the stability of Saturn’s rings. It had a massive nucleus, with electrons revolving around the nucleus, bound 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 Millikan determined charge and mass of an electron. (USA)

    Millikan measured the charge on an electron with his oil-drop apparatus. He also proved that this quantity was a constant for all electrons (1910), thus demonstrating the atomic structure of electricity. This means that we know that all the electrons in every atom has the same charge.
  • Ernest Rutherford demonstrated that the atom has an internal structure of a small, dense nucleus about which negatively charged electrons circle in orbits. (New Zealand)

    Rutherford formulated a model of the atom, which was like this: a very small positively charged nucleus, orbited by electrons. He also speculated on the existence of ‘neutrons’, which could somehow compensate for the repelling effect of the positive charges of protons by causing an attractive nuclear force and thus keeping the nuclei from breaking apart.Rutherford discovered the basic form of an atom regarding protons and electrons.
  • H.G.J. Moseley discovered mathematical relationship between wavelengths of X-ray and the atomic number. He also determined the charges on the nuclei of most atoms. (England)

    Moseley determined the charge of most nuclei 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 have different weights.
  • Niels Bohr developed an explanation of atomic structure that agrees with the periodic table of elements. (England)

    He suggested that when an atom is excited or heated, electrons can jump to higher levels, & when the atom cools, they drop down to lower levels, where precise quanta of energy are released as specific wavelengths. An electron’s energy levels can be imagined as concentric circles around the nucleus. He predicted the levels (or shells) had a maximum capacity of electrons each, the innermost being 2.This helps us understand why atoms release light and energy at certain frequencies.
  • James Chadwick discovered the neutron. (England)

    James Chadwick, an English scientist, used alpah particles in an experiment and discovered a neutral atomic particle with a mass close to a proton. Thus the neutron was discovered.