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Exploring Atomic Physics: A Beginner's Guide to the Structure of the Atom

This guide provides an introduction to atomic physics, covering key discoveries such as J.J. Thomson's identification of the electron and Rutherford's gold foil experiment, which revealed the positive nuclear core. The text explains the classical model's limitations, including questions about atomic stability and discrete energy levels. Emphasizing Bohr's model, it describes circular electron orbits, energy quantization, and photon interactions. Additionally, practical calculations for exciting hydrogen atoms are included, all aimed at fostering a foundational understanding of atomic structure and behavior.

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Exploring Atomic Physics: A Beginner's Guide to the Structure of the Atom

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Presentation Transcript

  1. Inside the atom A beginners guide to atomic physics

  2. Brief History JJ Thomson • Discovered the electron • Where is it? • Plum pudding Model • Rutherford • Gold foil experiment • Positive nuclear core

  3. Problems with classical model • Coulomb force could make electrons orbit nucleus like planets, BUT… • Accelerated charge is supposed to emit EM waves…why is atom stable? • Also, why do atoms emit and absorb only discrete frequencies of radiation?

  4. BOHR ATOM • Circular electron orbits • Only “stationary” orbits allowed • The energy of each orbit is given by: En= (-13.6 eV) 1/n2(where n is an integer) • Photons of the correct energy are absorbed, “exciting” the atom into a higher energy orbit • Photons are emitted when the electron makes a transition to a lower energy orbit • The energy of the photons corresponds to energy difference of the two orbits DE=hf

  5. Bohr atom (continued) Bohr atom...java applet • What wavelength of radiation would excite the hydrogen atom from the ground state (E1) to the third energy level? E1 = -13.6 eV/1 = -13.6 eV E2 = -13.6/9 = -1.5 Ev hc/l = 12.1 eV l = 1243 eV-nm / 12.1 eV = 100 nm

  6. What possible wavelengths of light could be emitted when a hydrogen atom “de-excites” from the 4th energy level? -0.82 eV -1.51 eV -3.4 eV -13.6 eV

  7. Stationary orbits • Conservation of energy: KE + PE = Etot ½ mv2 – ke2/r = Etotal • Circular motion: F=ma  ke2/r2 = mv2/r  ke2/r = mv2 • Combined: Etotal= mv2 – ½ mv2 = -½ mv2 OR Etotal = ½ ke2/r – ke2/r = -½ ke2/r

  8. Stationary orbits (continued) • Which orbits are allowed? • One way of getting the answer is to look at deBroglie wavelength of electrons. • l=h/mv • To “fit” in a particular orbit, 2pr=nl

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