Atom

History of an Atom

By Colo-NESCO
  • 403 BCE

    Democritus

    Democritus
    Democritus believed that atoms were uniform, solid, hard, incompressible, and indestructible and that they moved in infinite numbers through empty space until stopped.
  • Period: 400 BCE to

    Atom History

  • Indivisible

    Indivisible
    John Dalton has a theory that atoms are indivisible, just like the Greeks thought.
    -Tiny indestructible particles.
    -Atoms are indestructible, cannot be divided, cannot be created.
    -Chemical reactions are a rearrangement of atoms.
    -All atoms of a given element have identical mass and properties.

  • Cathode Ray Tube Experiment

    Cathode Ray Tube Experiment
    Showed that all atoms contain tiny negatively charged subatomic particles or electrons. J.J. Thomsen shot a beam of particles through a tube after making one side positive and negative. He looked to see which was the atoms bent towards with the beam of particles moving.

  • Thomsen "Plum Pudding Model"

    Thomsen "Plum Pudding Model"
    According to this model, the atom is a sphere of positive charge, and negatively charged electrons are embedded in it to balance the total positive charge. This was a structure with negatives being like plums.

  • Ernest Rutherford

    Ernest Rutherford
    Ernest Rutherford is very important to the history of the atom. He discovered that atoms had a tiny, dense, and positively charged core called the nucleus.

  • Gold Foil Experiment

    Gold Foil Experiment
    This experiment showed us that every atom has a nucleus where all of its positive charge and most of its mass is concentrated. They put a piece of gold foil and shot particles through it. If the Plum Pudding model was correct, they would be stopped. Since it was incorrect, they went straight through. Every once in a while, one would deflect off. Everyone once in a while, it would hit a nucleus which is why it deflected.

  • Niels Bohr

    Niels Bohr
    Niels Bohr had proposed a theory for the hydrogen atom, based on quantum theory that some physical quantities only take distinct values. Electrons move around a nucleus, but only in a specific orbit. If electrons jump to a lower-energy orbit, the difference is sent out as radiation. Bohr thought electrons circled the nucleus in orbit which is wrong. Bohr was right about energy levels.

  • Electron Cloud Model

    Electron Cloud Model
    Three guys came along. Heisenberg was one and he said electrons move so fast that once we know where we are, they're gone. Schrodinger used math to discover orbitals which is how electrons move. de Broglie said atoms move in waves.
    p+=proton
    n0=neutron
    e-=electron