History of the Atom

Aristotle and Plato

100

Plato believed that the world was made up of five regular solid, named "Platonic Solids".
Aristotle believed that the world was made up of the four elements: fire, air, water and earth. His theories about this was taught for 2000 years. He did not believe in Democrituses Atomic Theory.

Democritus

100

Democritus adopted the atomic theory from his mentor, Leucippus. The theory stated that “The universe is composed of two elements: the atoms and the void in which they exist and move.” Democrituses atomic theory also includes these points:
1. All matter consists of invisible particles called atoms.
2. Atoms are indestructible.
3. Atoms are solid but invisible.
4. Atoms are homogenous.
5. Atoms differ in size, shape, mass, position, and arrangement.

John Dalton

Jul 18, 1800

The main points of Dalton's atomic theory were:

1. Elements are made of extremely small particles called atoms.
2. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
3. Atoms cannot be subdivided, created, or destroyed.
4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
5. In chemical reactions, atoms are combined, separated, or rearranged.

J.J Thomson

Dec 7, 1880

J.J Thomson was a British physicist who discovered the electron. He discovered the electron using cathode rays and shooting them through air, noticing that it travelled further than the smallest atom ever could. From that he devised that atoms were made out of sub particles much smaller than atoms. He also found that the subparticles were negatively charged and theorized that atoms were held together by electrostatic forces, and that there must be a positively charged subparticle. Plum Pudding

Ernest Rutherford

Apr 22, 1900

Ernest Rutherford was the scientist responsible for the model of the atom where there is a positively charged nucleas and electrons orbiting the nucleus. The discovered that the nuclues of the atom is tiny in relatiom to the atom and that it is positively charged by firing alpha particles at a thin film of gold. He noticed that a small amount of the particles were reflected back or would change their course slightly. This showed that there was an extremely dense, positive nucleus in the atom.

Niels Bohr

Dec 15, 1922

Niels Bohr created the Bohr Model of the atom. He developed this model that shows the positively charged nucleus in the middle with electrons orbiting the nucleus through the experiments that Rutherford conducted. He also stated that the electron can be viewed as both a particle or a wave.