1. Democritus Occupation: Philosopher Dates of Discovery: 460 – 370 B.C. What was Discovered: That the world is made up of empty space and tiny particles called atoms How it Changed our Understanding of Matter: Matter can be broken into INFINITELY smaller pieces.

2. Antoine Lavoisier Occupation: French Chemist Dates of Discovery: 1782 What was Discovered: When chemical reactions occur, matter is neither created or destroyed. Law of Conservation of Matter How it Changed our Understanding of Matter: No matter what, you can’t make matter go away or appear. (Mass reactants = Mass products)

3. Joseph Proust Occupation: French Chemist Dates of Discovery: 1799 What was Discovered: Water is always 11% Hydrogen and 89% Oxygen by Mass How it Changed our Understanding of Matter: Atoms always have a fixed ratio in compounds (same # of elements compared to other elements; never changes in compounds)

4. John Dalton Occupation: School Teacher Dates of Discovery: 1766 -1844 What was Discovered: Created the Atomic Theory How it Changed our Understanding of Matter: 1. All matter is made up of atoms 2. Atoms are indivisible (can’t get smaller) 3. Atoms of the same element are exactly alike & different from atoms of other elements

5. J.J. Thomson Occupation: Physicist Dates of Discovery: 1897 What was Discovered: Electrons How it Changed our Understanding of Matter: Negatively charged parts of an atom (disproves that atoms are indivisible)

6. Hantaro Nagaoka Occupation: Physicist Dates of Discovery: 1909? What was Discovered: Proposed model in which electrons orbited around the nucleus How it Changed our Understanding of Matter: Presence of a nucleus of an atom

7. Ernest Rutherford Occupation: Scientist Dates of Discovery: 1911 What was Discovered: Nucleus How it Changed our Understanding of Matter: Found positively charged center to atoms called nucleus

8. Niels Bohr Occupation: Danish Scientist Dates of Discovery: 1885 - 1962 What was Discovered: Electrons have energy, constant motion around nucleus How it Changed our Understanding of Matter: Electrons aren’t found randomly around the nucleus (location depends on energy in electron)