Chem 14A 2010 Fall Midterm Solutions

What charge if any should be present to produce the

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What charge, if any, should be present to produce the most stable molecule or ion possible? What is the maximum bond order that such a molecule or ion could have? If the charge on the most stable species were increased or decreased by one, what would be the effect on the bond order? (8pt) The helium and hydrogen atoms have only their 1 s orbitals available for bonding. Combination of these two will lead to a σ and a pair of orbitals. The most stable species will be one in which only the σ σ orbital is filled. Thus we need a species that has only two electrons. The charge on this species will be +1. 2pt The maximum bond order will be 1. 2pt Adding one electron will decrease the bond order by 1/2 because an antibonding orbital will be populated. 2pt Taking an electron away will also decrease the bond order by 1/2 because it will remove one bonding electron. 2pt σ σ He 1s H 1s Q8B. Determine the bond orders for all of the following species and use them to predict which species of each of the following pairs has the stronger bond. (6pt) (a) C 2 + or C 2 2 C + (7 valence electrons): ( ) bond order = 1.5 1pt x y 2 2 2 2 2 2 2 ( * ) ( ) ( ) σ σ π π s s p p 1 , 2 , 1 1 2 C (8 valence electrons): bond order = 2 and is stronger 2pt x y 2 2 2 2 2 2 2 ( ) ( * ) ( ) ( ) σ σ π π s s p p (b) O 2 or O 2 + 2 O (12 valence electrons): , bond order = 2 1pt x y x y 2 2 2 2 2 1 2 2 2 2 2 2 2 ( ) ( * ) ( ) ( ) ( ) ( * ) ( * ) σ σ σ π π π π s s p p p p p 2 O + (11 valence electrons): bond order = 2.5 and is stronger 2pt x y x 2 2 2 2 2 2 2 2 2 2 2 ( ) ( * ) ( ) ( ) ( ) ( * ) , σ σ σ π π π s s p p p p 10
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  • Fall '10
  • Lavelle
  • Atom, Electron, TA, Molecule, λ, Constants and Formulas

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