Atomic Theory



450 bc

A Greek philosopher proposed that there were four fundamental substances:
Earth,Wind,Fire, and Water.


400 bc

Atomic theory states that all matter is made up of small units called atoms which can't be destroyed. Though that atoms were combined in a hook and eye system but we now know today that this isn't true


384 BC - 322 BC

That all matter was made of 4 elements. He believed that there were 4 qualities to these elements: dryness, hotness, coldness, and moisture

Daniel Bernoulli

1643 - 1644

Proposed air consists of tiny particulars that are to small to be seen and are loosely packed in space

Antoine Lavoisier

1743 - 1794

Laws of conservation of mass: father of modern chemistry

Joseph Louis Proust


Law of constant compositing in 1799 . He showed that the when chemical reactions occur, matter isn't destroyed, nor created

Joseph Priestley


Discovered oxygen,carbon monoxide, and nitrogen dioxide

John Dalton


States that elements consists of tiny particles called atoms and that all atoms of elements have identical properties. That compounds are elements which are joined together. He proposed a system of symbols to represent atoms of different elements

J.J Thomson

1856 - 1940

Calculated that mass to charge ratio. He also deducted that the electron was part of matter. He also introduced the Plum pudding structure and found electrons

Robert Millikans


Oil drip experiment measured an electrons charge

Earnest Rutherford

1909 - 1911

Revised and corrected Philip Leonard's theory. Stated that instead of having the positive and negative particles joined together. Discovered protons and that they are positively charged

Neils Bohr


Added to the atomic model that the outer shell of element could hold more electrons than the inner ones. Very similar to the modern atomic model

Evangelista Torricelli


Discovered that air had weight and can push down a column of mercury