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Atomic and Nuclear Physics

Atomic and Nuclear Physics. Topic 7. Atomic models. Videos :D. Properties of protons, neutrons and electrons. 1. + 1. nucleus. 1. 0. nucleus. outside nucleus. 0.0005. - 1. Nuclear notation. Nucleon number = mass number A = Z + N. Atomic number = number of protons. Terms .

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Atomic and Nuclear Physics

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  1. Atomic and Nuclear Physics Topic 7

  2. Atomic models • Videos :D

  3. Properties of protons, neutrons and electrons 1 + 1 nucleus 1 0 nucleus outside nucleus 0.0005 - 1

  4. Nuclear notation Nucleon number = mass number A = Z + N Atomic number = number of protons

  5. Terms • Page 150 in purple book. • Nucleon • Nuclide • Isotopes • Nucleon number (A) • Proton number(Z) • Neutron number A nuclide is a type of atom whose nuclei have specific numbers of protons and neutrons (both are called nucleons). Therefore, nuclides are composite particles of nucleons.

  6. Nuclear notation Number of protons PLUS neutrons (Mass number or nucleon number) 14 C Chemical symbol Number of protons (Atomic number) 6 An isotope of carbon consists of 6 protons and 8 neutrons. This can be written as: carbon 14 OR:

  7. Isotopes Isotopesare atoms of the same element (same atomic number) with different numbers of neutrons. The three isotopes of hydrogen hydrogen 1 hydrogen 2 (deuterium) hydrogen 3 (tritium) neutrons Note: The number after ‘hydrogen’ is the mass number of the isotope.

  8. Question 1 (a) (b) 13 60 N Co 7 27 (c) (d) 197 239 Au Pu 79 94 Determine the number of protons and neutrons in the isotopes notated below:

  9. Question 2

  10. Question 3

  11. Question 4

  12. Question 5

  13. The Plum Pudding Atomic Model Before about 1910 many scientists believed that an atom consisted of: Positively charged matter spread out like a pudding embedded by negatively charged electrons (like plums in a pudding). The ‘Plum Pudding’ Model

  14. Rutherford’s Atomic Model In 1909 Ernest Rutherford suggested that an atom consists of a a tiny positively charged nucleus surrounded by negatively charged electrons. Lord Rutherford 1871 - 1937

  15. Geiger & Marsden’s alpha particle scattering experiment In 1909 Hans Geiger and Ernest Marsden performed an experiment using alpha particles to determine which of the two models was the better in describing the structure of an atom. Geiger and Marsden

  16. The apparatus

  17. What was observed alpha source thin metal foil • Virtually all of the alpha particles went straight through the metal foil. • A few alpha particles were deflected through a small angle. • About 1 in 8000 were deflected backwards.

  18. How the results can be explained atom nucleus (highly enlarged) • Deflections occur because there is a force between the charged nucleus and the positively charged alpha particles. • Most of the alpha particles do not go near enough to the nucleus to be deflected. • Backwards deflections occur when the alpha particles make near head on collisions with the positively charged nucleus.

  19. How the results can be explained atom nucleus (highly enlarged) why isn’t the electron’s deflecting the alpha’s path?

  20. How their results supported Rutherford’s atomic model • The relatively small number of deflections indicates that most of the atom is empty space with only a very small nucleus. • The backward deflections can only occur if the nucleus is positively charged and contains most of the atom’s mass. • The ‘plum pudding’ model would not produce backward deflections.

  21. Bohr’s Model • Suggested electrons’ orbit the nucleus like planets orbiting the sun • If its circling the nucleus, what should then be between them? • What provides it?

  22. Bohr’s Model • Suggested electrons’ orbit the nucleus like planets orbiting the sun • If its circling the nucleus, what should then be between them? • Electrostatic force

  23. Bohr’s Model • Made a connecting between atom and light. • According to this model, electron’s only exist in certain orbits. • More radius (large orbit)  more energy in electron • When electrons drop orbits, this energy is released as light

  24. Bohr’s Model • Frequency of emitted light prop. to the change in energy • ΔE = E2 – E1 = hf • h = Plank’s constant = 6.6 x 10-34 Js

  25. Bohr’s Model • Remember the colors of light? • Which has the highest frequency? Energy?

  26. Bohr’s Model

  27. Spectra

  28. Emission Spectrum of Hydrogen

  29. Absorption Spectrum of Hydrogen

  30. Absorption Spectrum of Hydrogen

  31. Sodium emission spectrum

  32. Photons • What is light?

  33. Photons • What is light? A wave • Electrons can only occupy given energy levels. • Energy of the electron is said to be quantized. • When electrons move between orbitals they must emit or absorb energy. • Amount of energy depends on gap. • This energy is emitted or absorbed in “packets” of light called photons. • ΔE = E2 – E1 = hf • h = Plank’s constant = 6.6 x 10-34 Js • Each photon has a frequency that is proportional to the change of energy of the electron

  34. Aurora Borealis

  35. Question • Calculate the energy change required to produce a photon of red light of wavelength 700 nm. • Convert answer to eV.

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