Approx. 400 BC
- The first scientist to create a model of the atom.
- Created the name "atom" from the Greek word "atomos", which means uncuttable.
- He didn't know about a nucleus or electrons, all he knew was that everything is made of atoms.
- He had disagreed with Democritus's model of the atom
- He felt that there was no smallest part of matter and that different substances were made of earth, fire, air, and water.
- Thought there was no such thing as atoms.
- Discovered oxygen (which he called "dephlogisticated air".
- he Priestly Medal is the highest award given by to an American chemist by the Society.
- He had proposed the Combustion Theory which was based on sound mass measurements.
- Named Oxygen
- He also proposed the Law of Conversation of Mass which represents the beginning of modern chemistry.
- Lavoisier believed that matter was neither created nor destroyed in chemical reactions.
- John developed the concept of the mole and proposed a system of symbols to represent atoms of different elements.
- Dalton recognized the existence of atoms of elements and that compounds formed from the union of these atoms.
- He showed that at the same temperature and pressure, two volumes of hydrogen gas reacted with one volume of oxygen gas to produce two volumes of water (as a gas).
- Announced the law of combining volumes
- proposed what is now known as Avogadro's Hypothesis .
- The hypothesis states that at the same temperature and pressure, equal volumes of gases contain the same number of molecules or atoms.
- created the first periodic table
- The table was arranged according to increasing atomic weight and left holes for elements that were yet to be discovered.
- He brought forth the theory of relativity