1. Historical Atomic Models ABC II B Ms. Pollock Spring 2007

2. Democritus

3. Democritus’s Theory of Atomic Structure n First to propose atomic theory n 400 BCE n Atoms “atomos” are indivisible. n Leads to Aristotle’s belief that matter is made of 4 elements – earth, air, water, and fire

4. John Dalton

5. Dalton’s Atomic Theory n 1806 published theory n English teacher and climatologist n Quaker n Discovered color blindness n Very careful, repeatable measurements

6. Dalton’s Atomic Theory n Elements made of tiny particles, called atoms n All atoms of given element identical n Elements of different atoms different from each other n Atoms combined to make compounds n Atoms not able to be created or divided; only recombined in a reaction

7. William Crookes

8. Crookes’ Tube n Developed cathode-ray tubes –Control of electron beam –Discovery of new particles inside atoms n Device used in televisions n Discovery of thallium and helium

9. Crookes Tube

10. J. J. Thomson

11. Thomson and the Atom n Plum Pudding Model n Discovered electron in 1897 n Found cathode rays would bend toward positive charge, so must be negative

12. Ernest Rutherford

13. Rutherford’s Contribution n Discovered large positive charge in center of atom n Gold foil experiment n Discovered proton n 1909

14. Niels Bohr

15. Bohr Models n Electrons orbiting nucleus in special orbits n Nucleus very small n 1913 n Electrons only found in certain places in the atom

16. Albert Einstein

17. Einstein n Much energy released from small amounts of matter n E = mc 2 n Aided in development of atomic bomb n Connection of many physics theories and beliefs through one formula

18. Max Planck

19. Planck n Father of quantum mechanics n Energy not continuous, released in quanta n Developed universal constant of energy n Calculated energy based on electromagnetic frequency and constant