1. History of the Atom

2. 1.Democritus a) 1 st idea of atom – smallest particle The Greeks (~2500yrs ago) 2. Aristotle a)Observations, no experimentation b)All matter made up of 4 elements: Air, water, fire earth

3. 2. Antoine La Voisier 1743-1794 a)Discovered several elements b) Worked with law of conservation of mass c) Considered the Father of Modern Chemistry d) Beheaded during French Revolution

4. 3. John Dalton (1766 - 1844) a)Atomic Theory 1. Atoms are indivisible 2. All atoms of same element are identical BUT different than atoms of same element 3. Atoms combine in simple whole # ratios 4. Chemical rxns occur when atoms combine, split or rearrange

5. 4. Thomson, Sir J.J. (1856-1940) a)Cathode ray tube experiment (aka… raison bun or plum pudding model) 1.Set up a glass tube, free of air with magnets on each side 2.Sent a stream of particles thru it and observed which way they were deflected 3. Credited with discovery of electrons

6. 5. Ernest Rutherford 1871-1937 1.Set up screen with thin Au foil in front 2.Shot stream of alpha particles ( 4 2 He) thru 3.Most particles went straight thru, few deflected 4.Since 4 2 He is + charge, once deflected, it’s off of something else + 5.Credited with discovery of nucleus with + charge due to protons a) Gold Foil Experiment

7. 6. James Chadwick a)Discovered neutron 1. Same mass & location as proton

8. a)Solar system model of the atom 1.Electrons orbit nucleus in orbits called ENERGY LEVELS 2. Quantum – bundle of energy that an e - needs to change level 3.When e - change levels – not stable, they fall back towards nucleus & release energy in form of light that we see as colors (ROY G BIV) 7.Neils Bohr 1885-1962

10. 8. Schrödinger a)Quantum Mechanical Model 1. Deals with probability of where the electron is most likely located… Near the nucleus