The Atomic Theory

Democritus

400 BCE

Democritus was a Greek philosopher. He reasoned that if a stone was continuously cut into smaller and smaller pieces, it would become inseparable. He called this atomos. This is the Greek work for indivisible.

John Dalton

1803

John Dalton, unlike Democritus, had experimental evidence for this theory. His theory consisted of 4 major points. They were that matter is composed of atoms, atoms are different for all elements, atoms of different elements can combine into a compound, and that a chemical reaction is rearranging the atoms in a element.

J.J Thomson

1897

J.J. Thomson was the first of these philosophers to experiment with cathode ray tubes. This helped him figure out that atoms are combined of positive and negative charges, protons and electrons.

Ernest Rutherford

1911

Rutherford created a new experiment called the "gold foil" experiment. After his experiment he found that most particles were undeflected, a very small percent had bounced off at a large angle, and some particles were redirected back to the source. This helped him figure out that there is a tiny area in the atom that holds most of the weight and protons/neutrons. This was the nucleus.

Niels Bohr

1913

Bohr went out to fix a problem with Rutherford's model, and that is that the atoms should be unstable. He was able to figure out that electrons could jump from one orbit to another when gaining and losing negative charge.

Erwin Schrodinger

1921

The biggest difference of Schrodinger's model to Bohr's is that it is impossible to find an exact spot for an electron. This had led him to thought that electrons are found in areas called the electron cloud.