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Scientists. The atom. Democritus . - 400 BC- Greek philosopher - No experimenting Matter made up of indivisible particles = “ atomos ”. Dalton. 1801: Thomas Jefferson President 1802: John Dalton experimented and concluded…. 1806: Fall of Roman Empire . Dalton.
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Scientists The atom
Democritus - 400 BC- Greek philosopher - No experimenting • Matter made up of indivisible particles = “atomos”
Dalton 1801: Thomas Jefferson President 1802: John Dalton experimented and concluded…. 1806: Fall of Roman Empire
Dalton 1. Matter made up small particles= atoms • Cant be created, destroyed, or made smaller 2. Atoms of same element are identical • Different elements = different atoms 3. Chem. Rxn atoms separate, join, or rearrange 4. Atoms of different elements can combine in whole number ratios: compounds.
1850’s- Steam • Steam powered engines of ships, trains, & factories • Key Question’s of 19th Century= • “How to build more effective steam engines” and • “ How to predict behavior of steam at high temps and pressures.”
1896- Uranium - Uranium was found to emit strange energy: - Radioactivity: warm to the touch - Can unlock secrets to the atom
1898- Marie Curie Concluded Uranium atom gave off radiation ( but another chemist discovered first) Found Radium – led to cancer fighting drugs Won two Nobel Peace Prizes Found Polonium Kept radioactive materials in her pocket Died of leukemia from radioactive materials
1904-J.J. Thomson • Plum Pudding Model/ Chocolate Chip Cookie • Discovered electrons ( 1897) • Experiment with cathode ray tube • Particles move toward positive end • Particles must be negatively charged • Disproved that the atom was indivisible (could be broken into parts)
Rutherford’s Goldfoil Experiment Result: majority passed straight through some bounced @ large angles & straight back
1911-Rutherford • Discovered: • atom was mostly empty space • Atom had a dense positively charged center • Disproved the Plum Pudding Model • (he was a grad student of Thomson)
1913-Bohr • Planetary model of atom • Electrons move in an orbit • Each orbit had a definite energy
1926- Schrodinger • Extension of Bohr’s model • The electron “cloud” shows where the electron is most likely to be • You have a 90% chance of finding the electron • Electrons move like waves
History of Atomic Models Dalton 1802 Thompson 1904- “plum pudding” Rutherford 1911 Bohr 1913 “planetary model” Quantum mechanical model
1927- Heisenberg Uncertainty Principle Can not know the speed and the location of the e- at the same time
1932-Chadwick • Prisoner of war in WW1 • Worked for Rutherford • Discovered neutron • Issue: mass of helium was 4 but it only had 2 protons