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.

1800

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

1897

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

1900

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

1905

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

1919

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.

1912-1920

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.

1920

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.

1926

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.

1928

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

1932

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

1932

James Chadwick discovers the neutron.