chem lecture 14

chem lecture 14 - November 20, 8-9:20 AM (A00) or 5-6:20 PM...

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Chemistry 6A November 20, 8-9:20 AM (A00) or 5-6:20 PM (E00) Topics listed online (Ch.2, 3, and Fundamentals E,F) Same policies as ALL exams: - UCSD ID required - Calculator and pencil only on your person - No electronic devices Arrive early! Any additional materials must be placed at the front of the lecture hall.
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Chemistry 6A Consider the following molecule: Which statement is INCORRECT? (a) The hybridization on C is sp 2 (b) The hybridization for N is sp 3 (c) The molecule contains 5 σ bonds and 1 π bond (d) The 2 p orbital on O overlaps with the sp 2 orbital of C to form a π bond (e) Two of the sp 2 hybrid orbitals of O hold lone-pair electrons C H N O H H
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Chemistry 6A According to molecular orbital theory, which is the INCORRECT statement for C 2 ? a) There are 9 valence electrons in the molecular orbitals. b) The lowest unoccupied orbital (LUMO) is π * 2p . c) The σ 2p orbital has one electron. d) The molecule is paramagnetic. e) The bond order is 2.0.
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Chemistry 6A 4 The following 6 molecular orbitals belong to F 2 . Identify each MO and arrange the set in order of increasing energy. A B C D E F
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Chemistry 6A The six π MOs formed from six 2 p atomic orbitals in benzene are shown in the cartoons below and labeled from left to right as A-F. What is the correct ordering of these molecular orbitals, from lowest to highest energy ? A B C D E F (a) A < C = F < D = E < B (b) B < A = F < D = E < C (c) C < A = B < D = F < E (d) F < A = B < C = D < F (e) B < A = C < E = F < D
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Chemistry 6A 6
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Chemistry 6A 7 How do we understand the meaning of a weighted-average atomic mass? How do we relate relative masses on the atomic scale to absolute masses on the gram scale? How are chemical formulas determined?
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Chemistry 6A 8 • We use a relative atomic mass scale in which 12 C is the standard: it is assigned a mass of exactly 12 atomic mass units (amu) • An atomic mass unit (amu, u) is exactly 1/12 of the mass of a single carbon atom. 1 amu = 1.9926465 x 10 -23 g / 12 = 1.66054 x 10 -24 g • Relative to this standard, the masses of all other atoms are measured by use of mass spectrometry Historically (since Dalton’s time), atomic masses have also been referred to as atomic weights , which are dependent on g. So, if carbon-12 has a mass of 12 amu, why is the listed atomic mass of carbon 12.011?
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Chemistry 6A 9 The atomic mass of an element is a weighted average of all its naturally occurring isotopes . Carbon has three isotopes:
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chem lecture 14 - November 20, 8-9:20 AM (A00) or 5-6:20 PM...

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