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The Evolution of Atomic Theory: From Mendeleev to Quantum Physics

This overview captures the key milestones in atomic theory, beginning with Mendeleev's Periodic Table in 1869 and the introduction of the mole, Avogadro's number, and atomic models. It details the discovery of the electron, the work of Rutherford and Bohr on atomic structure, and developments in radioactivity by Becquerel and the Curies. Significant contributions to particle physics, including the neutron, neutrino, and cosmic rays, illustrate the transition to modern quantum theory, highlighting the intricacies of matter and the fundamental forces that govern atomic interactions.

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The Evolution of Atomic Theory: From Mendeleev to Quantum Physics

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  1. The measure of things

  2. Periodic system (Mendeleev, 1869) NAvogadro = 6.022 x 10 23 /mole  mH = 1.673 x 10 -24 g

  3. electron shell nucleus A = atomic number Z = number of electrons . = number of protons A-Z = number of neutrons Atomic model Rutherford-Bohr

  4. Discovery of the electron 1896: Zeeman discovers influence of magnetic field on spectral lines e/m 1897: Thomson deflects cathode rays e/m (similar experiments by Kaufmann, Wiechert) 1899: Thomson determines charge e (cloud chamber) electron mass m ≈ 1/2000 mH

  5. Cathode rays Geissler tube Crookes CRT

  6. Deflection of cathode rays by electric fields

  7. Radioactivity: Becquerel (1896) - Discharges an electroscope - M. Curie: atomic property - E. Rutherford (1899): 2 types:  rays (short range)  rays (long range) - M. + P. Curie: e/m  rays are electrons (1900) - E. Rutherford:  rays are 2+ helium ions (1908)

  8. The atomic nucleus Geiger & Marsden (1909-10): scattering of -particles from metal foil (gold, platina) Rutherford (1911): Atoms are almost empty, all mass and positive charge concentrated in a tiny central nucleus

  9. Hydrogen spectrum Balmer (1885): Bohr (1913): quantum theory of spectral lines

  10. Compton effect Elastic scattering of massless photon with electron (initially at rest)  particle nature of photon

  11. Atomic mass M (~ Z) grows faster than atomic number A  not only protons in nucleus Chadwick (1932): neutron  + 9Be  12 C + n

  12. The neutrino -decay of neutron: half-life: 15 min _ n  p + e + e- (Pauli, 1930)

  13. Cosmic rays Theodor Wulf (1909): Spontaneous discharge of electroscope Victor Hess (1911-13): Balloon flights Radiation intensity increases at heights > 4 km

  14. Cosmic ray airshowers (Pierre Auger, 1936)

  15. Anti-matter e- + e+  2  E = me c2 = 0.511 MeV Anderson discovers positive anti-electron (positron) (1932)

  16. New particle families    +  (Powell, 1947) Mass (MeV/c2): 135 - 140 105 495 Pion: (+ , 0 , -) Muon: -, + Kaon: (K+, K0), (K-, K0) _

  17. Hadron spectrum _ _ _ K Spectrum explained by quark structure: p = (uud), n = (udd),  =(ud), K = (us), …

  18. Nucleons Proton Neutron Charge: + e 0 e quarks Charge: + 2/3 e - 1/3 e

  19. Three families: 1897-2000 Particle masses in MeV; 1 MeV  1.81027 gram

  20. Binding forces Electrons: electric Coulomb force (photons) Nucleons: Yukawa forces (pions, not elementary) Quarks: color forces (gluons) e,q , g e,q

  21. Classification of matter particles Charge +2/3, -1/3 0, -1 Quarks: strong interactions, (u, d) Leptons: no strong interactions, (, e) Universality in quark-lepton spectrum: Weak interactions <---> transmutation Charged exchange bosons: W+,W- Neutral exchange boson: Z

  22. Weak vector bosons: W±, Z0 µ µ - u d _ W- e e- µ = 2.2 x 10-6 s in rest frame Note (Einstein): moving clocks go slow t = (v)  ( (v) > 1 )

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