Exam 1 Key - Chem 10181 Fall 2007(1 EXAM 1 KEY 1 Carbon and...

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Chem 10181, Fall 2007 EXAM 1 KEY September 27, 2007 1 (1) Carbon and oxygen combine to form carbon monoxide, CO. Some properties of C and O are given in the table below: Species Ionization Energy (kJ/mol) Electron Affinity (kJ/mol) C 1086.4 122 O 1313.9 141 (a) (4 pts.) Give the ground-state electron configuration for O, and state how many unpaired electrons are present in a ground-state O atom in the gas phase. 1s 2 2s 2 2p 4 There are two unpaired electrons. (b) (7 pts.) Oxygen has a higher ionization energy and a higher electron affinity than carbon. Explain this difference in terms of atomic structure. As one moves to the right in the periodic table, the number of protons in the nucleus increases, and they are not completely screened by the added electrons, leading to an increase in Z eff and a decrease in the energy of the orbitals. Lower-lying orbitals mean that electrons are more difficult to remove (higher IE) and more favorable to add (higher EA). (c) (12 pts.) On the next page, sketch the MO diagram for the diatomic molecule CO. Remember to place the relevant atomic orbitals on the outside of the diagram, the molecular orbitals on the inside, and clearly label all orbitals. Finally, fill the MO diagram with the number of electrons appropriate for CO. See next page. Note that the orbitals for O are below those for C (since O is more electronegative, see part (b)). S-p mixing is significant, since the C 2s orbital will be quite close to the O 2p orbital.
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Chem 10181, Fall 2007 EXAM 1 KEY September 27, 2007 2 (c) Your molecular orbital diagram for CO goes here 2s 2p z 2p y 2p x π * 2px π * 2py π 2px π 2py σ 2s(2p) σ∗ 2s(2p) σ 2p(2s) σ∗ 2p(2s) C O CO 2s 2p x 2p y 2p z
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Chem 10181, Fall 2007 EXAM 1 KEY September 27, 2007 3 (d) (6 pts.) The bond distances for CO, CO + , and CO are given in the table below. Fill in the
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This homework help was uploaded on 04/17/2008 for the course CHEM 10181 taught by Professor Brown during the Fall '08 term at Notre Dame.

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Exam 1 Key - Chem 10181 Fall 2007(1 EXAM 1 KEY 1 Carbon and...

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