1. Unit 2 – Atoms, Elements, & Compounds This unit will cover portions of chapters 14, 15, & 16

2. Atomic Time Line The next series of slides gives you a brief history of we have come to understand the structure of the atom. Like the lab yesterday, we cannot see what is inside.

3. Leucippus & Democritus – 400 BC First definition of the atom.  The smallest part of a thing, that still is that thing.  Examples.

4. John Dalton – Early 1800s Famous for his atomic theory.  1. Each element is made of atoms.  2. All atoms of an element are identical.  3. Atoms of different elements have different properties such as mass and density.  4. Atoms cannot change during a reaction.  5. Compounds are formed from two or more atoms.  6. Compounds are defined by proportions.

5. John Dalton – Early 1800s Dalton’s picture of the atom?  Very small spheres that were solid.

6. J.J. Thomason - 1897 Discovered the electron by accident.accident  We can conduct this experiment today.  We have to review a bit of atomic interactions. + and + - and – + and –

7. J.J. Thomason - 1897 Thomason’s picture of the atom?  Plum pudding model or today?

8. Hantaro Nagaoka - 1904 Figured out that electrons are moving around the center of the atom, like planets do around the sun.

9. Hantaro Nagaoka - 1904 Planetary model

10. Ernst Rutherford - 1911 Gold Foil ExperimentExperiment

11. Ernst Rutherford - 1911 Gold Foil Experiment Results

12. Ernst Rutherford - 1911 Conclusion  Atom is mostly empty space.  What is at the middle, must be positive.  Discovered the proton and named the nucleus.

13. Neils Bohr - 1913 Electrons move in energy levels.  When an electron moves between energy levels, it gives off some energy, a.k.a., light.  Each element has a unique display of colors.

14. Neils Bohr - 1913

15. James Chadwick - 1932 Saw that atoms were twice as heavy as they should be. p’se’sn’s charge mass

16. James Chadwick - 1932 Atomic Models – always 3D

17. Modern Picture of the Atom The atomic cloud