1. Rev 6/7/06 1807 1896 1903 400 BC 1911 19131932 Atomic Model Development

2. Democritus – 400 BC Defined an Atom as the smallest unit of a material that can not be split up Greek word “atom” means invisible Atoms are solid, homogeneous, indestructible and indivisible

3. Dalton’s Atom - 1807 Atom = Solid sphere All elements are composed of tiny invisible particles called atoms Atoms of same element- alike & different from atoms of other elements Atoms join together in whole number ratios to form compounds.. that means they join in a definate proportion every time the same compound is formed.

4. Henri Becquerel 1896 © Discovered radioactivity © Radiation produced spontaneously by unstable atomic nucleus

5. Thomson’s Atom - 1897 Discovered electrons Plum Pudding model (for us Americans it looks like a chocolate chip cookie model) Electrons - charge + charge “pudding”

6. Rutherford’s Atom - 1909 discovered dense positively charged nucleus using gold foil experiment electrons protons Gold Foil Animation

7. James Chadwick 1932 Identified neutron Same mass as proton No charge

8. electrons orbit in energy levels around the protons in the nucleus. p+p+ Bohr’s atom - 1913 like our solar system… (electrons the planets, the nucleus the sun!)

9. Atomic Time Line review… 1807 1896 1903 400 BC 1911 19131932 - Atom -Modern Atom -Radioactivity-Electron -Positive Nucleus -Energy Levels-Neutron