1. 7: Atomic and Nuclear Physics 7.1 The Atom

2. Atomic Theory The Plum Pudding Model Negative charged electrons Positive charged mass

3. Rutherford’s Alpha Particle Scattering Experiment

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25. Results Rutherford found out that... 1. Most of the alpha particles passed through the gold foil undeviated. 2. A few alpha particles were deflected from their path but continued through the gold foil. 3. A small number of alpha particles rebounded.

26. Conclusions 1.As most alpha particles passed through the gold foil atoms undeviated, Rutherford concluded that most of the atom was actually empty space. 2. The deviation of some alpha particles from their original path were due to positive charges within the foil. 3. A very small number of alpha particles had rebounded because they collided with something with a much bigger mass, which contains a concentrated region of positive charge. This is now called the nucleus.

27. The Rutherford - Bohr Model of the Atom n n

28. Energy Levels E.g. E = hf h= Planck constant = 6.6 x 10 -34 m 2 kgs -1 hf = E 2 - E 1

29. Emission Spectra (Line Spectra) Hydrogen... Helium... Neon...

30. Limitations of the Bohr Atom Electron ‘probability cloud’:

31. The Nucleus Any nuclide can be represented in the following way: A = nucleon number Z = proton number X = symbol for the element N = neutron number Q. Nucleons must experience a force other than electrostatic force. Why? X A Z

32. Isotopes Nuclide: an atomic nucleus with a particular combination of protons and neutrons. Isotope: Atoms with the same number of protons but different numbers of neutrons. E.g.1 E.g.2 37 17 35 17 HydrogenDeuteriumTritium

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