Part 1. Multiple Choices (24) Because nuclei are much heavier than electrons, on
ID: 591860 • Letter: P
Question
Part 1. Multiple Choices (24) Because nuclei are much heavier than electrons, one can separately solve Schrüdinger equations of electrons and nuclei. This is a statement of 1. A. Pauli exclusion principle B. Hund rule C. Bohr's theory D. Born-Oppenheimer approximation 2. How many normal vibrational modes (or vibrational degree of freedom) doets CH3CI have? A) 15 B) 12 C)9 D) 10 3. Provided that SO; has no pure rotational spectrum, which is the most possible molecular structure for SO2? A) Linear S-0-0 B Linear O-S-O C) Bent S-0-O D) Bent O-S-o 4. The bond order of N2 is A)3 B) 2 C)2.5 D) 1.5 A) N2 = N2+ B) N2 > N2+ C) N2Explanation / Answer
1) D, Born-Oppenheimer approximation which states that the electronic and nuclear degrees of freedom are nearly separable. This is a good approximation because the electrons are much lighter than the nuclei, so they move much faster and can rearrange themselves to a stable configuration almost as soon as the nuclei move. Hence, to a good approximation, one can fix the nuclei at a given set of coordinates and solve for the probability distribution of the electrons; this is called the ``electronic structure'' problem.
2) C, Chlormethane (CH3Cl) has 9 Normal Vibrational Modes as follows :
1. Vibrational mode 1a degenerated 1/calc = 3096 cm-1 (Raman + IR active)
2. Vibrational mode 1b degenerated 1/calc = 3096 cm-1 (Raman + IR active)
3. Vibrational mode 2 1/calc = 2998 cm-1 (Raman + IR active)
4. Vibrational mode 3a degenerated 1/calc = 1430 cm-1 (Raman + IR active)
5. Vibrational mode 3b degenerated 1/calc = 1430 cm-1 (Raman + IR active)
6. Vibrational mode 4 1/calc = 1328 cm-1 (Raman + IR active)
7. Vibrational mode 5a degenerated 1/calc = 991 cm-1 (Raman + IR active)
8. Vibrational mode 5b degenerated 1/calc = 991 cm-1 (Raman + IR active)
9. Vibrational mode 6 1/calc = 712 cm-1 (0 active)
3) D, SO2 has bent structure with Sulphur is placed in between two oxygens like O-S-O (but bend) due to more electronegativity of oxygen attracts electrons towards itself and which leads to a bend structure.
4) C, Bond Order of N2:
Total number of electrons:13
Electronic Configuration=:1s² *1s² 2s² *2s² 2py² [2pz² 2px1 ]
Bond Order=[9-4]/2=5/2=2.5
5) A, By MOT they both have same bond order of 2.5
6) A, CO2 has no possibility of pure rotational spectrum.
7) No Idea about the answer, Sorry.
8) A, Bond length is directly proportional to rotational energy.
9) C, Rotational Spectrum- Microwave and Vibrational Spectrum- Infrared
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