Studied black body radiation.

Realized that light can not be just any amount of energy, but only discrete units called quanta.

Received the Nobel Prize in 1921 for his work on the photoelectric effect.

Discovered the electron in 1897.

Proposed the plumb pudding or watermelon model.

His model had a sea of positive charge with electrons scattered within.

Performed the gold foil experiment.

Shot positive alpha particles into thin sheets of gold. The some of the alpha particles went straight thru and others reflected back.

Was the first to propose that the atom had a concentrated positive center (the nucleus).

Proposed the electron cloud theory.

Proposed a model in which the location of electrons can be anywhere around the nucleus, but are most probable at the Bohr orbits.

His model of the atom explained atomic spectrum.

His model explained why atoms emit light only at particular frequencies.

His model of the atom had a concentrated positive nucleus and electrons in certain orbits (but never in between these orbits).

In his model photons occur because electrons fall from exact orbits to lower orbits.

Proposed that atoms were hard spheres.

Was the first to propose that matter had a smallest unit, called "atomos".