1. Atomic Theories

2. Greek 2000 yrs ago Democratis - different shapes and sizes. Smallest piece can be obtained All atoms made of same material.

3. John Dalton 1803 Atoms of different element are not alike. Compounds are formed from atoms of 2 or more elements. Atoms cannot be divided.

4. John Thompson 1897 Atom has a (+) charged “pudding” Discovered “electrons” are scattered inside pudding Atoms can be divided Atoms have an overall neutral charge Received Nobel

5. Ernest Rutherford 1911 (+) charges are inside the nucleus (-) electrons are outside the nucleus Performed “Bullet” experiment

6. In 1911, Rutherford deduced from these results that almost all of the mass of an atom, an object so small that it would take over five million of them side-by-side to cross a full stop on this page, is concentrated in a nucleus a thousand times smaller than the atom itself. (If the orbital electrons in our atoms were compressed into the nucleus we would occupy the space of a small grain of sand.) The nuclear model of the atom had been born. Rutherford’s Bullet Experiment

7. Niels Henrik Bohr 1913 Electrons move in orbits around the nucleus Electrons are found at the certain distances from nucleus

8. Wave Modern Electrons don’t move around in a definite path. We can only predict where an electron might be.