mar 1, 1778 - Antoine de Lavoisier
Lavoisier made a huge impact on modern chemistry. He defined an element as a pure substance that can't chemically be broken down into a simpler substance. He also made a huge difference by discovering 23 new elements. All of Lavoisier's investigations were based on his exact measurements and observations. Lavoisier believed air was made up of two gases, oxygen and another one, One of them burns and one does not. His theory that the air was made up of two gases was wrong because air is actually made up of multiple gases.
Added to timeline:
The Atomic Theory