1. Atomic Timeline
By Emma Divers

2. 440 B.C.
Democritus was a Greek Philosopher who lived around 440 B.C. He discovered that atoms are small, hard particles that are constantly moving. He also learned that atoms are unable to be broken.

3. 1803
John Dalton discovered that all substances are comprised of atoms. He composed experiments and found out that atoms of the same element are the exact same and that atoms made of different elements are different. His theory stated that elements combine in specific proportions. He did this by conducting experiments by combining elements.

4. 1897
J.J Thomson conducted the cathode-ray tube experiment and discovered that there are small, negatively charged particles within the atom. Thomson also created the “plum-pudding” model to demonstrate his theory of the atomic structure.

5. 1911
Earnest Rutherford conducted the gold foil experiment. He discovered that the nucleus is small, dense, and positively charged, and that most of the mass of an atom is in the nucleus. He also stated that the electrons (negatively charged subatomic particles) move in the empty space of the atom. This led him to believe that most of an atom is comprised of empty space.

6. 1913
In 1913 Niels Bohr discovered that electrons travel in a definite path. He also made the discovery that electrons are capable of jumping between levels from path to path.

7. Twentieth Century
Erwin Schrodinger and Werner Heisenberg challenged Bohr to say that electron paths are unable to be predicted. These two men also discovered that electrons can’t be found in paths, but in electron clouds.