Atomic Theory Timeline


Leucippos - Said that all matter is composed of tiny inseparable particles

500 BC

Alchemist- Developed the theory that all metals are composed of mercury and sulfur and that it is possible to change base metals into gold.

500 BC - 1720

Democritus- His atomic theory anticipated the modern principles of the conservation of energy and the irreducibility of matter

442 BC

Aristotle- Thought there were only four elements: water, earth, air, and fire

384 BC - 322 BC

Dark Ages

500 - 1500

Paracelsus- He was the first to shape reshape the essence of earth, air, fire, and water to chemicals


George Stahl- Developed the Phlogiston theory which basically means, when something burned, it lost phlogiston to the air.


Robert Boyle- His law describes the relationship between volume and absolute pressure of gas at which the temp is kept the same within closed system


Carl Scheele- Before Priestly Scheele discovered oxygen first and called it,“fire air” because it supported combustion.

1770 - 1773

Priestly- Found that air was made up of a mixture of gases and one that was oxygen which he called "dephlogisticated air".


Lavoisier- Considered the founder of modern chemistry, developed the theory that elements cannot be broken down by any means and that chemical compounds are made from elements


Joseph Proust- Law of Definite Proportions states that a compound is composed of exact proportions of elements by mass regardless of how the compound was created


John Dalton- thought that atoms of the same atom are the same and atoms of different elements are not, believed that compounds are made of two atoms.