Greek Philosophers believed that everything was made up of the Four elements. Earth, Air, Fire, and Water. These ideas lasted until around 492 B.C. when Democritus Proposed his ideas of the "Atom".
Democritus
Democritus was a Greek philosopher who came up with the idea of Atomos. These ideas were proposed around 492 B.C. Although these ideas were dismissed they did lead to later discoveries almost 2000 years later
Dalton
Dalton was an English School Teacher who revised Democritus' ideas and Propsed them in 1808. His ideas were accepted and were the basis for scientists. His Atom was a spherical shape just like Democritus'.
Thompson
Thompson is responsible for our knowledge of the Electron. He discovered the electron by experimenting with a Cathode Ray Tube and realized the last model of the atom didnt account for the negative particles. These discoveries were made in 1897.
Rutherford
Rutherford is responsible for the newest model in 1911. During a gold Foil experiment, Rutherford discovered that there were electrons orbiting the nucleus and protons that make up the nucleus.
Chadwick
Chadwick discovered the neutron in 1932. He was trying to prove Rutherford's theory when he put an excessive charge in the nucleus and discovered that some particles remained unaffected.,
Bohr
Bohr is the scientist that started our ideas that the electrons have a specific layer that they belong to. In 1913 He suggested that an atom that has a small positively charged nucleus and electrons that travel in a classical pattern around the nucleus.
ECM
The ECM, or Electron Cloud Model was the latest model in 1926. Erwin Schrödinger built upon Bohr's model and thought of the possibility that electrons could be in a cloud around the nucleus in their designated energy levels.
Quantum Mechanical Model
This model shows the specific paths that electrons could be in. This is the basis of modern day chemists and physicists