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Spectroscopy for AP Chemistry

Spectroscopy for AP Chemistry. Photoelectron Spectroscopy (PES) Provides data for ionization energy trends and applications Mass Spectrometry Provides atomic/molar mass data as it ionizes. Electron Configuration.

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Spectroscopy for AP Chemistry

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  1. Spectroscopy for AP Chemistry • Photoelectron Spectroscopy (PES) • Provides data for ionization energy trends and applications • Mass Spectrometry • Provides atomic/molar mass data as it ionizes

  2. Electron Configuration Is there any direct evidence that this diagram is accurately showing potential energy of electrons on the atom?

  3. Photoelectron Spectroscopy Atom Ephoton = hv KE = mv2 2 Monochromatic Beam of X-Rays e- IEelectron = Ephoton - KE

  4. Photoelectron Spectrum Each peak is relative to the others. This indicates the relative number of electrons. If the peak is twice as big, there are twice as many electrons. Relative Intensity = 2 Relative Intensity = 1 20 MJ/mol 10 MJ/mol 0 MJ/mol

  5. Photoelectron Spectrum Valence 19.3 MJ/mol 1.36 MJ/mol RI = 2 RI = 2 Gap is due to increased energy of the orbital (decreased amount of energy to remove the electron) 0.80 MJ/mol RI = 1 20 MJ/mol 10 MJ/mol 0 MJ/mol

  6. Photoelectron Spectrum Boron (Z=5) 19.3 MJ/mol 1.36 MJ/mol • Analysis: • Valence has 2 values: sp • RI is 2 to 1 in valence: s2p1 • Closest core has RI 2 not 6: not pxs2p1 • s2s2p1 must be 1s22s22p1 RI = 2 RI = 2 0.80 MJ/mol RI = 1 2s2 1s2 2p1 20 MJ/mol 10 MJ/mol 0 MJ/mol Inner orbitals require the most energy Valence orbitals require the least energy

  7. Photoelectron Spectrum • Depending on the size of the table, 1s may be intentionally cut out of view because it’s too far away and makes the graph too long • Remember IE is about REMOVING electrons, which means they are removed from the OUTSIDE to the INSIDE, and NOT in reverse order of energy! For example, 4s is removed BEFORE 3d.

  8. Photoelectron Spectrum 2p6 Sodium (Z=11) 3.67 MJ/mol 1s2 2s2 3s1 104 MJ/mol 6.84 MJ/mol 0.50 MJ/mol { } 8 MJ/mol 4 MJ/mol 0 MJ/mol

  9. Online PES Resources http://www.chem.arizona.edu/chemt/Flash/photoelectron.html https://www.youtube.com/watch?v=NRIqXeY1R_I https://www.youtube.com/watch?v=vANbxozsRSA

  10. Assign sublevels to the peaks, and identify the element

  11. From the AP Sample Questions…

  12. From the AP Sample Questions…

  13. Which peaks in the photoelectron spectrum are representative of the binding energy of p orbital electrons? • C only c. C and E • D only d. B, C and D

  14. Peaks A, B, and C represent the binding energies of electrons in which subshells of neon? • a. 1s,2s,2p b. 2p,2s,1s • c. 1s,1s,1s d. 2s,2p,2p

  15. 2. Which of the following statements best accounts for peak A being far to the left of peaks B and C: a. the electron configuration of neon is 1s2 2s2 2p4 b. neon has 8 electrons located in its valence shell c. core electrons of an atom experience a much higher effective nuclear charge than valence electrons d. peaks B and C show first ionization energies of electrons in, whereas peak A shows the second ionization energy of neon electrons

  16. 3. Which of the following statements best accounts for peak C being three times the height of peak B: a. the intensity of the photoelectron signal at a given energy is a measure of the number of electrons in that energy level b. electrons represented by peak B have approximately triple the binding energy than those represented by peak C c. in a photoelectron spectrum, as binding energy increases the relative number of electrons decreases d. the height of peaks in a photoelectron spectrum does not have any relation to the structure of an atom

  17. Analyzing data from PES 2.0 2p 1s 2s Relative Number of Electrons 4.7 84.0 + 9080706050403020100 Binding Energy (MJ/mol) • Which of the following elements might this spectrum represent? • He (B) Ne • (C) N (D) Ar

  18. Analyzing data from PES 7.9 2p6 3p1 1s2 2s2 3s2 Relative Number of Electrons 151 12.1 1.09 0.58 100101 Binding Energy (MJ/mol) Given the spectrum above, identify the element and its electron configuration: • B (B) Al • (C) Si (D) Na

  19. Real Spectra

  20. Mass Spectrometry • Mass spectrometry gives the mass to charge ratio • Like PES, the relative size of the peaks indicates the relative number of particles • Separates isotopes according to mass • Used to find relative abundance and atomic/molar mass of unknown samples

  21. Mass Spectrometry

  22. From the AP Sample Questions… The elements I and Te have similar average atomic masses. A sample that was believed to be a mixture of I and Te was run through a mass spectrometer, resulting in the data above. All of the following statements are true. Which one would be the best basis for concluding that the sample was pure Te?

  23. From the AP Sample Questions… • Te forms ions with a -2 charge, whereas I forms ions with a -1 charge. • Te is more abundant that I in the universe. • I consists of only one naturally occurring isotope with 74 neutrons, whereas Te has more than one isotope. • I has a higher first ionization energy than Te does.

  24. Based on the mass spectrum of atom Y, which of the following statements is false? • a. peak A and peak D come from atoms that have the same number of electrons • b. there are seven isotopes of atom Y • c. peak C comes from the most abundant isotope of atom Y • d. peak D comes from an atom with 4 more protons than the atom that gave peak B

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