Atomic Theory

Democritus

400 BCE

400 BC:
Democritus, a Greek philosopher theorizes that all things are made from small indivisible particles that are shaped in different ways to form materials.

John Dalton

1808

Similarly to Democritus, John Dalton believed that all substances were made up of indivisible, sing units. Where they differed was when John Dalton tested the ratios of how many elements go into certain compounds. With this data, he theorized that most substances were made up of multiple "atoms" instead of just one type of atom.

JJ Thompson

1904

JJ Thompson discovered the electron by testing certain elements with a high voltage electric and and detirmened if the substance was attracting or reppelling the arch and he detirmened some substances were negativley charged. He theorized that electrons were inside of an atom surrounded by a posotivly charged substrate balancing the charge. His idea resembled a plum pudding muffin.

Ernest Rutherford

1911

Ernest Rutherford discovered an atom's nucleus by firing alpha particles at a piece of gold foil. He expected them to just pass right through but instead, a small percentage flew off in odd angles. proving that there was a substantially dense mass in the atom.

Neils Bohr

1913

Neils Bohr discovered that electrons circle the atom on different levels called orbitals. He found out that electrons can jump to different levels by absorbing photons, or energy. When the electrons lose this energy they jump back down and release it.

Erwin Schrödinger

1926

Erwin Schrödinger's model refined Bohr's by instead of showing where the electron was while it orbited his shows where the electron is by probability. He also theorized that orbitals had different shapes for the energy levels.