1. Bellwork10/12/06 How long have people been interested in understanding matter and its structure? A.Thousands of years B.Hundreds of years C.A few years D.Never

2. History of Atomic Structure

3. Ancient Philosophy Who: Democritus When: 460-370 b.c.e. Where: Greece What: Democritus believed that matter was made of small particles he named “atoms”. Said they were solid, homogeneous, and couldn’t be divided Atoms of different elements have different sizes, shapes and properties Why: Democritus used observation and inference to explain the existence of everything.

4. Aristotle When: 334-322 B.C.E. Aristotle believed in 4 elements: Earth, Air, Fire, and Water. No such thing as empty space

5. Aristotle Democritus

6. Particle Theory Who: John Dalton When: 1808 Where: England What: Described atoms as tiny particles that could not be divided or destroyed. Thought each element was made of its own kind of atom that were exactly the same in size and mass. Atoms of elements can combine to form compounds Why: Building on the ideas of Democritus in ancient Greece.

7. John Dalton

8. Sir William Crookes Cathode Ray tube Found that electricity had a negative charge Late 1800’s

9. Discovery of Electrons Who: J. J. Thompson When: 1897 Where: England What: Thompson discovered that electrons were smaller particles of an atom and were negatively charged. Plum pudding model Why: Thompson knew atoms were neutrally charged, but couldn’t find the positive particle.

11. J. J. Thompson

12. Robert Millikan Early 1910s Found the charge and mass of electrons 9.1x10 28.0000000000000000000000000091g

13. Atomic Structure I Who: Ernest Rutherford When: 1911 Where: England What: Conducted an experiment to isolate the positive particles in an atom. Decided that the atoms were mostly empty space, but had a dense central core. Gold foil experiment. Why: He knew that atoms had positive and negative particles, but could not decide how they were arranged.

15. Ernest Rutherford

16. Atomic Structure II Who: Niels Bohr When: 1913 Where: England What: Proposed that electrons traveled in fixed paths around the nucleus. Scientists still use the Bohr model to show the number of electrons in each orbit around the nucleus. Why: Bohr was trying to show why the negative electrons were not sucked into the nucleus of the atom.

17. Niels Bohr

18. Electron Cloud Model Electrons travel around the nucleus in random orbits. Scientists cannot predict where they will be at any given moment. Electrons travel so fast, they appear to form a “cloud” around the nucleus.

19. Electron Cloud Model

20. Atomic Structure Timeline Requirements: Must include a title. Must include a spot for each of the 7 items. Must include at least the Who, When, and What. Must have a picture (color is preferred) for each item. Options: 1.Comic book format 2.Standard timeline