1. History of Atomic Structure

2. Ancient Philosophy Who: Aristotle, Democritus When: More than 2000 years ago Where: Greece What: Aristotle believed in 4 elements: Earth, Air, Fire, and Water. Democritus believed that matter was made of small particles he named “atoms”. Why: Aristotle and Democritus used observation and inferrence to explain the existence of everything.

3. Aristotle Democritus

5. Alchemists Who: European Scientists When: 800 – 900 years ago Where: Europe What: Their work developed into what is now modern chemistry. Why: Trying to change ordinary materials into gold.

6. Alchemic Symbols

7. Particle Theory Who: John Dalton When: 1808 Where: England What: Described atoms as tiny particles that could not be divided. Thought each element was made of its own kind of atom. Why: Building on the ideas of Democritus in ancient Greece.

8. John Dalton

9. Solid, Tiny Particle

10. 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. Why: Thompson knew atoms were neutrally charged, but couldn’t find the positive particle.

11. J. J. Thompson

13. Electron Charge and Mass Who: Robert A. Millikan (1868-1953) When:1910 Where: United States What: Found the quantity of an electron charge in his oil-drop experiment. He calculated the charge by suspending negatively charged oil droplets between two plates and measure the rate of fall when the voltage was changed. Why: Wanted to discover whether electrical charge occurred in a specific amount.

14. Robert Millikan

15. 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. Why: He knew that atoms had positive and negative particles, but could not decide how they were arranged.

16. Ernest Rutherford

19. 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.

20. Niels Bohr

21. HELIUM ATOM + N N + - - proton electron neutron Shell What do these particles consist of?

22. Electron Cloud Model-1920s 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.

23. Electron Orbitals Who: Erwin Schrödinger When: 1926 Where: Austria What: Develops mathematical equations to describe the motion of electrons in atoms, which leads to the quantum mechanical model Why: Wanted to better understand the movement of the electrons in an atom

24. Erwin Schrödinger

25. Electron Cloud Model

26. Birth of Quantum Mechanics: Who: Werner Heizenberg When: 1925 Where: Germany What: Proposed that electrons traveled in atomic orbitials Why: Heizenberg realized that the reason Bohr’s model failed was that it was trying to predict none observable variables (position, speed)

27. 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 3.Flip Book