Timeline Of The Evolution Of The Atomic Theory

The Greek philosophers, Democritus and Leucippus theorized that the world was made up of tiny particles called atoms. The word atom means indivisible in Greek.

Aristotle thought differently than Democritus; he thought that the world was made up of air, water, fire, and earth, instead of tiny particles. Aristotle's ideas were used by the Catholic church in the middle ages, and the people who followed Democritus, were shunned or killed.

Newton formed a theory of light, that light was made up of particles. He also formed the three laws of motion.

1)If an object is moving at a constant speed, it won't move unless you force it to speed up or slow down.

2)The acceleration of an object depends on the strength of the overall force applied to it as well as on the mass of the object.

3)With every action, there is a reaction

John Dalton believed in Democritus' work. His theory consisted of four basic ideas:
1) All matter is composed of atoms that are indivisible.
2) All atoms are identical in properties, such as size and mass.

3) Atoms are rearranged as a chemical reaction occurs.
4) Compounds are formed by combination of multiple atoms.
5) They cannot be created or destroyed.

In 1886, Goldstein helped contribute to the events that lead to the discovery of the proton. He observed the changes in a cathode ray tube, and discovered the anode rays, positively-charged particles that moved in the opposite direction, from the anode to the cathode. His work helped Rutherford.

In 1897, J.J. Thomson discovered the electron. His work proved one of Dalton's ideas wrong, the atom was not indivisible, but in fact made up of multiple components. The discovery was made when he conducted an experiment with a cathode ray tube, when an electrical current was passed through, glowing material could be seen. When he put two electrically charged plated on opposite ends of the tube, the light was bent on the positive plate. Thomson thought that the atom looked like raisin pudding, a ball with negative electrons clumped on it.

Called the father of quantum physics, invented the quantum theory. Quantum physics is mathematical interaction between particles in matter. Einstein used the quantum theory.

He disliked Thomsons model of the atom, and created his own. A model that resembled Saturn with its rings; the rings were the electrons and the sphere was the positive center. Hantaro's model was not accurate, and it was left to Bohr and Rutherford to fix that.

Millikan is credited for finding the charge and mass of an electron. He did so by conducting the oil drop experiment in 1909. he put a charge on a tiny drop of oil, and measured how strong an electric field had to be, to stop the oil drop from falling. The mass was 9.10938291 × 10 ^-28 grams, and the charge was -1.

In 1908, Ernest Rutherford proved Thomson's atomic model to be incorrect. He is famous for his gold foil experiment which stated the existence of protons. He shot alpha particles at the gold foil, and observed where they hit. Most were undeflected, while the rest bounced off in different directions.