Download What is the inside of an atom like? Geiger

1P22/1P92 (2011) Chapter 29 Atoms and Molecules
Friday, January 14, 2011
10:03 AM
What is the inside of an atom like?
Geiger-Marsden experiment (1909)
Rutherford's atomic model (1911) --- a good step, but it was
NOT quantitative
• one of the lessons/methods of science: look for the
unexpected
Also, Rutherford's model suffered from a fatal flaw: according
to classical electromagnetic theory (Maxwell's equations),
atoms should emit continuous (that is, a wide range of
wavelengths) electromagnetic radiation (they don't; rather
they emit "line spectra"), and they should be unstable
(electrons should lose energy as they emit electromagnetic
radiation, and eventually spiral into the nucleus, where they
would die a dramatic death upon joining forces with the
protons in the nucleus), which they aren't. So, although it was
clear that Rutherford was onto something, it was also very
clear that his model was wrong.
Enter Niels Bohr.
- Bohr's atomic model; see pages 960 ff in the textbook
What are line spectra?
• emission and absorption spectra:
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Exercises
CP 3 The Paschen series is analogous to the Balmer series,
but with m = 3. Calculate the wavelengths of the first three
members in the Paschen series. Which part(s) of the
electromagnetic spectrum are these in?
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CP 10 The allowed energies of a simple atom are 0.0 eV, 4.0
eV, and 6.0 eV. (a) Draw the atom's energy-level diagram.
Label each level with the energy and the principal quantum
number. (b) Which wavelengths appear in the atom's
emission spectrum? (c.) Which wavelengths appear in the
atom's absorption spectrum?
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CP 12 A researcher observes hydrogen emitting photons of energy
1.89 eV. What are the quantum numbers of the two states involved
in the transition that emits these photons?
Consider instead the related problem where we use
CP 13 A hydrogen atom is in the n = 3 state. In the Bohr
model, how many electron wavelengths fit around this orbit?
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- the idea of electron energy levels and "shells" was later
adapted to help describe atomic nuclei as well
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Exercises
CP 26 Predict the ground-state electron configurations of
Mg, Sr, and Ba.
CP 31 Explain what is wrong with each electron configuration.
(a) 1s22s22p83s23p4
(b) 1s22s32p4
CP 30 Identify the element for each electron configuration.
Then determine whether this configuration is the ground state
or an excited state.
(a) 1s22s22p63s23p64s23d9
(b) 1s22s22p63s23p64s23d104p65s24d105p66s24f145d7
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CP 34 Hydrogen gas absorbs light of wavelength 103 nm.
Afterward, what wavelengths are seen in the emission
spectrum?
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