History of the atom

Democritus

450 BCE

Democritus wondered what would happen if matter was cut in half into smaller bits intill it could not be cut anymore. He called the uncutable bits atomos, which were random shapes.

John Dalton

1800

Dalton revives Democritus idea of the atom, he theorized that everything was made of atoms and that atoms of the same material have the same weight and vice versa. He also said that atoms join together to make compounds. His model of the atom is called the chocolate chip cookie model.

J. J. Thomas

1897

He finds evidence of electrons by sending electric current through a vacuum tube, showing it had a negative charge. Knowing that atoms have a neutral charge, saying that there is the negative charge and the rest of the atom is positively charged. He said that an atom is like a plum pudding, which has plums scattered through it. Which is why his model is the plum pudding model.

Ernest Rutherford

1911

In 1899, Rutherford discovered that some elements give off positively charged particles. He named them alpha particles. He did an experiment with gold foil where most particles went through, some bounced back or were slightly bounced back. This showed that the nucleus had positive particles in it and that some of the atom was empty space. Rutherford made the planatery atom model

Neils Bohr

1913

Bohr created the current model of the atom that is still used today. This model is called the planetary model, for it looks like planets orbiting the nucleus. He also said that the electrons have energy levels for which they orbit and the number in each shell goes up. In order to jump levels they must absorb energy to go up or release energy to go down.