Aristotle had his own beliefs on the world, he believed that earth, air, water, and fire were the four main elemnets. he also beleived that if you cut matter in hhalf yoou would just end up with a smaller peice of matter (this is wrong).
Democrtius was the first person tyo realize that matter can not be broken up any smaller. He used the term "Atomos" to describe these particles. His ideas were unpopular at the time, but were the first step towards Atomic Theory.
He discovered the motions of of planets. He also believed that atoms were held together by forces.
He developed the "Boyle's Law." It is where he discovered the relationship between pressure and volume.
Joseph Priestly discovered dephlogisticated air which we now know as, Oxygen.
Antoine Lavoiser, otherwise known as The Father of Science. He discovered that the Phlogiston Theory was wrong and he also discovered and named the elements oxygen and hydrogen.
He discovered the amount of electrons that could be in an atom.
Harriet Brooks is most famous for research on nuclear transmutations and radioactivity. She is one of the first people that discovered radon and she also tried to figure out the atomic mass of it.
He rearranged the periodic table by the atomic number instead of the atomic mass.
He was famous for his model of the atomic theory. The models wwere similar to the rings on Saturn