How we got to where we are now Atomic Theorists How we got to where we are now

Law of Conservation of Mass Who: Antoine Lavoisier Matter can't be created or destroyed When: 1785 Where: France

Law of Definite Proportions Who: Joseph Proust Compounds – Elements put together in fixed ratios of small whole numbers C + O2  CO2 When: 1797 Where: France

Law of Multiple Proportions Who: John Dalton Two elements can form more than one compound The subscripts of the elements in the compounds will be small whole numbers. C + O2  CO2 C + O2  CO Where: England When: 1803

Who: Aristotle What: All matter is a combination of fire, air, earth or water When: 350 B.C. Where: Greece

Who: Democritus When: 400 B.C. Where: Greece What: Matter was made of indivisible substances he called atomos (1st talk of the atom)

Who: John Dalton What: Solid Sphere Model (1st atomic theory) Elements are made up of indivisible particles called atoms Each element was composed of the same kind of atoms. Different elements were composed of different kinds of atoms. Compounds are composed of atoms in specific ratios. Atoms are not created or destroyed in a reaction. When: 1805 Where: England

Problems with Dalton’s Theory Today (issues that weren’t known about ..yet) Matter is composed of indivisible particles There are electrons, protons and neutrons All atoms of a particular element are identical There are isotopes 3. Different elements have different atoms Atoms combine in whole number ratios Atoms can’t be created or destroyed Nuclear explosions destroy matter

Who: J.J. Thomson What: Atoms aren't smallest particle Conducted experiment with a Cathode Ray Tube Particles had a negative charge (discovered electrons) Model = plum pudding When: 1897 Where: England

Cathode Ray Tube

Who: Robert Millikan What: Experiments to determine mass of electron Conducted the oil drop experiment Verified that electron is negatively charged; 1.6 x 10 -19 coulombs No new model Where: America When: 1910

Millikan Oil Drop Experiment

Who: Ernest Rutherford What: Conducted Gold Foil experiment Proved nucleus is dense, positively charged core of atom When: 1911 Where: America Model = Stationary Planetary

Rutherford’s Experiment Gold Foil Experiment

Results of foil experiment if Plum Pudding model had been correct.

What Actually Happened

Who: Niels Bohr What: Pulsating Planetary Model Electrons can move between energy levels When: 1913 Where: Denmark

There were many people involved with developing the mathematical process to determine the path of the electron. One of these men was Schroedinger. What: pulsating orbital model When: 1926 Where: Switzerland

Who: James Chadwick What: Confirmed existence of neutron No new atomic model When: 1932 Where: England