Lecture 20 - Chemical bond

Lecture 20 - Chemical bond - Midterm Exam 2 Wed, Mar 2,...

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Unformatted text preview: Midterm Exam 2 Wed, Mar 2, 2011 1:10 2:00 pm 198 Young (last name begins with A- M) 176 Everson (last name begins with N- Z) Exam covers Chapters 10.1 10.5, 11, and 12. Closed Book and Closed Notes No electronic devices except calculator Practice Midterm on course website At least one assigned homework problem will appear on the exam. Review session on Tue Mar 1 at ?. Problem set 2 grades on website and returned during TA office hours. Molecular Orbital Theory (LCAO-MO) Molecular orbitals arise from linear combination of atomic orbitals (LCAO): ( ) B B A A * c c = A + B A -- B ( ) B B A A c c + = Anti-bonding orbital ( *) Bonding orbital ( ) No electron density repulsion attraction A B MOs for 1 st Row Diatomics H H Stable bond He He Unstable bond = 1s = 1s = 1s = 1s H 2 (2 e- ): ( 1s ) 2 He 2 (4 e- ): ( 1s ) 2 ( * 1s ) 2 Bond order = (2 0) = 1 Bond order = (2 2) = 0 bonding orbital ( 1s ) anti-bonding ( * 1s ) BO for H 2- ( 1s 2 * 1s 1 ): http://en.wikipedia.org/wiki/Bond_order BO for H 2 + ( 1s 1 ): BO for He 2 + ( 1s 2 * 1s 1 ): Calculate bond order (BO) for H 2 + , H 2- , and He 2 + and predict which is most stable. ( ) MO g antibondin the in e MO bonding the in e order bond = # # 2 1 BO = (1 0) = 1/2 BO = (2 1) = 1/2 BO = (2 1) = 1/2 H 2- or He 2 + Bonding ( 1s ) Anti-bonding ( * 1s ) 2s 2s 2s + 2s s 2 2 nd Row Sigma ( ) MOs 2p z + 2p z 2p z- 2p z p 2...
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Lecture 20 - Chemical bond - Midterm Exam 2 Wed, Mar 2,...

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