Atomic theory

By Thundaevans
  • 800 BCE

    Democritus

    Democritus
    Discovered:that all matter is made up of small indestructible units he called Atoms
    observed :that the universe is composed of two elements and contributed :help people understand the concept of an atom

  • John Dalton

    John Dalton
    Observed: all elements consisted of atoms
    Discovered: how atoms interacted and the weight contributed that each mass and size were based on on its element
    Contributed: each mass and size wee different based on its element

  • E. goldstein

    E. goldstein
    Discovered: canal rays
    Observed: canal rays which have positive charge equal to an electron
    Contributed: led to the discovery of a proton

  • J.J. Thompson

    J.J. Thompson
    Discovered: Studied "canal rays" were actually electrons
    Observation: He was investigating a long-standing puzzle known as "cathode rays.
    Contribution : the rays were made up of electrons.mysterious rays are streams of particles much smaller than atoms, that are minuscule pieces of atoms.

  • Rutherford

    Rutherford
    Discovered alpha beta and gamma rays in radiation.
    Observations: properties of each element could be defined by this number. Each element could then be assigned and atomic number
    contributed: the Rutherford model of an atom which sparked the idea of neutrons in the atom

  • Milikan

    Milikan
    Discovered: identified the negatively charged electron in the cathode ray tube
    Observed:the electron was a component of all matter and calculated the charge to mass ratio for the electron.
    Contribution:came as a result of his oil-drop experiment, which measured an electron's charge.

  • Henry Molsley

    Henry Molsley
    Observed:x-ray specs Chad to study atomic structure
    concluded:that there were three unknown elements between aluminum and gold
    Contribution:Moseley was able to determine the number of positive charges in the nucleus of an atom. The first form of atomic number

  • Neil's Bohr

    Neil's Bohr
    Discovered: electrons stay in stable orbits around the atomic nucleus but can jump from one energy level to another.
    Observed: observed an atomic structure theory that showed the outer orbit of an atom could hold more electrons than the inner orbit
    Contributed:by the Bohr model of an atom Electrons should move around the nucleus but only in prescribed orbits.

  • De brogelie

    De brogelie
    Discovered that electrons had a dual nature-similar to both particles and waves. Particle/wave duality.
    Observations: worked on extensions of wave mechanics
    Contributions that electrons could behave as waves under some conditions

  • Schrodinger

    Schrodinger
    Discovered: introduced "wave mechanics" as a mathematical model of the atom.
    Observations: Viewed electrons as continuous clouds and introduced
    Contributions used mathematical equations to describe the likelihood of finding an electron in a certain position.

  • Chadwick

    Chadwick
    Discoveries:Using alpha particles discovered a neutral atomic particle with a mass close to a proton
    Observations:joined Rutherford in accomplishing the transmutation of other light elements by bombardment with alpha particles,
    Contributed:to the discovery of the neutron

  • Works cited

    Buescher, Lee. "Atomic Structure Timeline." Atomic Structure Timeline. N.p., n.d. Web. 02 Nov. 2016. Type, By Print. "Barcodes,Inc." A Timeline on Atomic Structure. N.p., n.d. Web. 02 Nov. 2016.