History of Atoms

Democritus

400 BCE

He thought that if you took an object and kept cutting it in half, at some point you will end up with something that can't be cut. Democritus thought that atoms were shaped the way their objects were. For example, he thought that sweet things were made of smooth textured atoms, while bitter things were made of sharp atoms.

John Dalton

1803

John Dalton thought that each element had its own atom. He described atoms as tiny,hard balls.He also proposed that atoms couldn't be split into pieces. The model of an atom for Democritus and Dalton didn't change at all.

J.J. Thomson

1904

Thomson discovered that atoms had electrons, or a negatively charged particle inside of an atom. He called the atom itself a positively charged cloud and inside were negatively charged electrons. The model changed from just a ball to a cloud with electrons inside.

Ernest Rutherford

1911

Rutherford described the atom with two parts, a positively charged nucleus and electrons orbiting the nucleus. He thought the atom was mostly empty and the electrons orbited the nucleus, like planets do to a sun. His model changed, because know there was a nucleus and an orbit of electrons, and not just a ball like Thompson's idea.

Niels Bohr

1913

Niels Bohr expanded on Rutherford's model, but his model showed the electrons circling the nucleus not orbiting randomly. In his model he said that the electrons have a fixed amount of energy in them, determined by the circles.

Heisenberg/Schrodinger

1926

Heisenberg said that we couldn't determine the exact spot of the electrons, so in their model there is a cloud of electrons. Their model consisted of a nucleus with multiple protons and neutrons, and a cloud of electrons. The electrons are somewhere inside the cloud.