History of an Atom

By: Michelle Kim

600 B.C.

Thales of Miletus discovers that bits of hair and other light objects attract to a piece of Amber after rubbing the piece of Amber with fur.

460 B.C.

Democritus creates a "theory" of atoms.


John Dalton experiments with chemicals that seem to consist of lumpy particles, which were atoms.


J.J. Thomson proposes the structure of atoms and discovers electrons.


Max Planck discovers quanta, which is when you see how much energy is in an atom by heating it.


Albert Einstein explains that the light being absorbed into the atom can release electrons, called the photoelectric effect.


Rutherford identifies the nucleus as particles of discrete positive charges of matter. He named those particles proton. He also found hat protons had a 1836 times the mass of an electron.


Neil Bohr creates a theory that electrons don't spiral into the nucleus.

He made two rules that went along with this theory;

1) Electrons can only orbit the nucleus at a certain distance

2) Atoms radiate energy when an electron jumps from a higher-energy orbit to a lower-energy orbit. Also, an atom absorbs energy when an electron gets boosted from a low-energy orbit to a high-energy orbit.


Neil Bohr and Arnold Sommerfield created a model that shows that electrons can move in certain orbits, orbits can have different shapes (circular or elliptical) and that orbits tilt in the presence of a magnetic field.


Erwin Schrödinger experimented to see the outcome of the model of the atom on the basis that atoms were particle waves and created the symbol psi.


Paul Dirac created a bunch of equations that predicted that there was a positive charged electron.


Carl Anderson proves Paul Dirac's theory by discovering a anti-electron with a cosmic ray.


James Chadwick discovers the neutron.