1. Development of Atomic Structure 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. Democritus (ca. 450 BC)

3. 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 inference to explain the existence of everything.

4. 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.

5. Alchemic Symbols

6. John Dalton (1766-1844)

7. Dalton’s Atomic Theory (18030 1) All matter is made of atoms. Atoms are indivisible and indestructible. 2) All atoms of a given element are identical in mass and properties 3) Compounds are formed by a combination of two or more different kinds of atoms. 4) A chemical reaction is a rearrangement of atoms.

14. Wilhelm Roentgen (ca. 1895)

16. Henri Becquerel

18. Marie Curie ca. 1920. Inset: Pierre Curie (Marie's favorite picture of her husband).

20. Ernest Rutherford

24. Rutherford Scattering: Nuclear Model Rutherford scattering probes the atom. (Hit it with something!) –Beam of  particles (He 2+ ) strikes a thin gold metal foil. –Atoms in the foil scatter the alpha particles through various scattering angles  that are detected with a scintillation screen. –180º scattering can occur (“back bounce”), indicating a “hard core” interaction between the a particles and atoms in the foil. “Nuclear” model by Rutherford explains large scattering angles.