1. Radiation Protection and Safety 11/15/2015 1 Atomic Structure   Dalton – law of definite proportions   Avogadro – equal volumes of gas   Balmer – visible spectrum of H   Thomson – charge to mass ratio of cathode rays Electrons have less mass than hydrogen atoms “Plum pudding” model

2. Radiation Protection and Safety 11/15/2015 2 Atomic Structure   Rutherford – scattering of alpha particles Atoms are mostly empty space R nucleus ~ 1.3A 1/3 x 10 -15 m   Forces: Coulomb vs. nuclear   Accelerating charges emit EM radiation Why are electrons in atoms accelerating? What is wrong with Rutherford’s model?

3. Radiation Protection and Safety 11/15/2015 3 Atomic Structure   Bohr – model of single electron systems Discrete, stable electron orbits Photon emission or absorption Matches observed spectra of H

4. Radiation Protection and Safety 11/15/2015 4 Atomic Structure   Why does Bohr’s theory not explain all systems? Quantized variables Non-circular orbits Relativistic effects   As n → ∞, quantum and classical theories match. Bound states of H get closer together as n increases   Wave-particle duality of light and matter Diffraction, Interference Compton effect, photoelectric effect