2. I. Atomic History A.Democritus (460-370 BC) 1.Ancient Greek philosopher 2.Proposed matter was made of tiny indivisible particles 3.He called them atoms

3. B. John Dalton (1766-1844): 1. Teacher and amateur scientist 2. Proposed Dalton’s Atomic Theory a. Everything is made of atoms which are indestructible b. Atoms of the same element are identical c. Compounds are made of 2 or more atoms d. Chemical reactions are rearrangements of atoms

4. C. J.J. Thomson (1856-1940) 1. Discovered electron in 1897 2. Proposed a model of the atom 3. It looked like a bunch of negatively charged raisins sitting in some pudding

5. D. Ernest Rutherford (1871-1937) 1. 1911 conducted experiment with gold foil and alpha particles 2. Lead to discovery of atomic nucleus and protons 3. Proposed more familiar model of atom

6. E. James Chadwick (1891-1974) 1. Discovered neutron in 1932 2. Later worked as head of English team on the Manhattan Project