The History of The Atom

By Alison_Ansorg
  • 460 BCE

    Democritus

    Democritus
    In 460 BCE, Democritus was the first recorded curiosity about the atom. He thought to himself, "What would happen if I broke this cheese in half into the smallest pieces I could?" He determined that what the smallest particles would be were called atoms.

  • John Dalton

    John Dalton
    In the early 1800's, John Dalton continued Democritus's theory and he discovered the four main ideas of atomic theory. These are that all matter is made of atoms that are invisible and indestructible,
    that all atoms in a singular element hold the same mass and properties, that compounds are two or more atoms combined, and finally that a chemical reaction is a rearrangement of atoms.

  • Marie Curie

    In 1895-98, Marie Curie discovered the radioactive elements we see on the periodic table today. Such elements as uranium, polonium, and radium ar ethe ones she discovered.

  • J.J. Thompson

    J.J. Thompson
    In 1897, J.J. Thompson discovered the electron. He did this by using high voltage and different metals to determine positive and negative charges. He then determined that electrons had a negative charge, and matter hasd a positive charge.

  • E. Goldstein

    In 1900, E. Goldstein discovered protons. He did this by using his logic that by the laws of electricity, if electrons have a negative charge, and atoms are neutral, there must be a positive force also acting within that atom. Thus he concluded that protons must be that force.

  • Robert Millikan

    In 1910, Millikan discovered the magnitude of an electron’s charge. Using electrified oils and metal plates, he discovered how negatively-charged electrons are compared to protons.

  • Ernest Rutherford

    Ernest Rutherford
    In 1911, Ernest Rutherford discovered the nucleus. He did this by using an alpha particle scattering technique to determine that most of an atom is empty space with a "heavy" weight in the middle.

  • Niels Bohr

    Niels Bohr
    In 1912, Bohr discovered the modern model of the atom we know today, minus the neutrons. He created the well-known nulceus in the middle with the shell of electrons orbiting around it.

  • Quantum Mechanical Model (aka Wave Model)

    Quantum Mechanical Model (aka Wave Model)
    Discovered by Erwin Schrödinger in 1926, the Wave Model of the atom includes an electron cloud instead of determined orbits. This more accurately represents what an atom might look like, as the electrons are moving so fast and are transferring to different orbits so quickly that it would appear more like a cloud.

  • James Chadwick

    In 1932, Chadwick discovered the neutron. He realized this by using a similar technique to that of Rutherford, with alpha particle scattering. These new neutral particles changed the atom's modern model to what it is today.