1. Atomic Numbers

2. Henry Moseley (1887 - 1915) “Moseley, as it were, called the roll of the elements, so that for the first time we could say definitely the number of possible elements between the beginning and the end, and the number that still remained to be found.”

3. Ions in Water Solution

4. Mass Spectra Mass Spectroscope Francis William Aston (1877 - 1946)

5. Modern Mass Spectroscope

6. Hydrogen Spectrum

7. Atomic Weights of Some Isotopes ElementIsotopeAtomic Weight Hydrogen 1H1H1.007825 2H2H2.01410 Helium 4He4He4.0026 Carbon 12 C12 (exactly) 13 C13.00335 Oxygen 16 O15.99491 17 O16.9991 Neon 20 Ne19.99244 21 Ne20.99395 22 Ne21.99138 Chlorine 35 Cl34.96885 37 Cl36.9659 Uranium 235 U235.0439 238 U238.0508

8. Mass Number (A) Isotopic Mass (amu) % Abundance 196195.1650.14 198197.96710.04 199198.96716.83 200199.96823.12 201200.97013.23 202201.97029.79 204203.9736.85 Mercury Spectrum

9. Atomic Number Atomic Weight

10. Atomic Structure Worked with: Hans Geiger Ernest Marsden Ernest Rutherford (1871 - 1937)

11. Gold Foil Experiment

12. Then I remember two or three days later Geiger coming to me in great excitement and saying, “We have been able to get some of the alpha particles coming backwards…” It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it cam back and hit you.

13. Radioactive Elements Pitchblende Pierre and Marie Curie

14. Large Nuclei