The History of The Atom

Democritus

400 BCE

Democritus was the first to coin the term "atom" from the Greek "atomos" meaning indivisible.

Aristotle

330 BCE

Aristotle believed in 5 basic elements (earth, water, fire, air, aether) He also did not believe matter was made of smaller particles.

John Dalton

1803

Dalton's Theory of the Atom says that atoms are small particles that cannot be created or destroyed. He said that atoms can combine in fixed ratios to form compounds.

William Crookes

1875

William Crookes set up an experiment using a glass tube and running an electric current through. When hooked up to a battery, a green light ran through the beam, this proved that particles exist.

J.J. Thompson

1897

Set up Crookes experiment to prove that the glow was not caused by light but actual atoms that were charged. From this experiment he found the electron.

Ernest Rutherford

1909

Set up an experiment to see if Thompson's model was right. Some beams went through, but others bounced back in unexpected angles which told him that the atom is mostly empty space and the center, which he called the nucleus, held positive particles called protons.

Niehls Bohr

1913

Found that electrons are not simply surrounding the nucleus but they travel around the atom in energy levels, shells, or orbits.

Werner Heisenberg

1925

Heisenberg stated that you cannot know both the speed and position of an electron at the same time.

James Chadwick

1925

James Chadwick found the other particle in the nucleus that has mass, the neutron.