Problem 5
Suggest an appropriate hybridization scheme for the central atom in each of the following species: (a) \(\mathrm{SiF}_{4}\); (b) \(\left[\mathrm{PdCl}_{4}\right]^{2-} ;(\mathrm{c}) \mathrm{NF}_{3} ;(\mathrm{d}) \mathrm{F}_{2} \mathrm{O} ;(\mathrm{e})\left[\mathrm{CoH}_{5}\right]^{4-}\); \((\mathrm{f})\left[\mathrm{FeH}_{6}\right]^{4-} ;(\mathrm{g}) \mathrm{CS}_{2} ;(\mathrm{h}) \mathrm{BF}_{3}\).
Problem 7
(a) \(\mathrm{PF}_{5}\) has \(D_{3 \mathrm{h}}\) symmetry. What is its structure? (b) Suggest an appropriate bonding scheme for \(\mathrm{PF}_{5}\) within VB theory, giving appropriate resonance structures.
Problem 8
(a) Draw the structure of \(\left[\mathrm{CO}_{3}\right]^{2-}\). (b) If all the \(\mathrm{C}-\mathrm{O}\) bond distances are equal, write a set of resonance structures to describe the bonding in \(\left[\mathrm{CO}_{3}\right]^{2-}\). (c) Describe the bonding in \(\left[\mathrm{CO}_{3}\right]^{2-}\) in terms of a hybridization scheme and compare the result with that obtained in part (b).
Problem 9
(a) Is \(\mathrm{CO}_{2}\) linear or bent? (b) What hybridization is appropriate for the \(C\) atom? (c) Outline a bonding scheme for \(\mathrm{CO}_{2}\) using the hybridization scheme you have suggested. (d) What \(C-O\) bond order does your scheme imply? (e) Draw a Lewis structure for \(\mathrm{CO}_{2}\). Is this structure consistent with the results you obtained in parts (c) and (d)?
Problem 10
What is meant by a ligand group orbital?
Problem 11
\(\mathrm{VB}\) and \(\mathrm{M} \mathrm{O}\) approaches to the bonding in linear \(\mathrm{XH}_{2}\) (X has \(2 s\) and \(2 p\) valence atomic orbitals) give pictures in which the \(\mathrm{X}-\mathrm{H}\) bonding is localized and delocalized respectively. Explain how this difference arises.
Problem 16
The I-I bond distance in \(\mathrm{I}_{2}\) (gas phase) is \(267 \mathrm{pm}\), in the \(\left[\mathrm{I}_{3}\right]^{+}\) ion is \(268 \mathrm{pm},\) and in \(\left[\mathrm{I}_{3}\right]^{-}\) is \(290 \mathrm{pm}\) (for the \(\left[\mathrm{AsPh}_{4}\right]^{+}\) salt). (a) Draw Lewis structures for these species. Do these representations account for the variation in bond distance? (b) Use MO theory to describe the bonding and deduce the I-I bond order in each species. Are your results consistent with the structural data?
Problem 17
(a) \(\mathrm{BCl}_{3}\) has \(D_{3 \mathrm{h}}\) symmetry. Draw the structure of \(\mathrm{BCl}_{3}\) and give values for the bond angles. \(\mathrm{NCl}_{3}\) has \(C_{3 \mathrm{v}}\) symmetry. Is it possible to state the bond angles from this information? (b) Derive the symmetry labels for the atomic orbitals on \(\mathrm{B}\) in \(\mathrm{BCl}_{3}\) and on \(\mathrm{N}\) in \(\mathrm{NCl}_{3}\).
Problem 21
\(\operatorname{In}\left[\mathrm{B}_{2} \mathrm{H}_{7}\right]^{-}(5.11),\) each \(\mathrm{B}\) atom is approximately tetrahedral. (a) How many valence electrons are present in the anion? (b) Assume that each \(\mathrm{B}\) atom is \(s p^{3}\) hybridized. After localization of the three terminal \(\mathrm{B}-\mathrm{H}\) bonds per \(\mathrm{B}\), what B-centred orbital remains for use in the bridging interaction? (c) Following from your answer to part (b), construct an approximate orbital diagram to show the formation of \(\left[\mathrm{B}_{2} \mathrm{H}_{7}\right]^{-}\) from two \(\mathrm{BH}_{3}\) units and \(\mathrm{H}^{-}\). What does this approach tell you about the nature of the \(\mathrm{B}-\mathrm{H}-\mathrm{B}\) bridge?
Problem 22
(a) What hybridization scheme would be appropriate for the Si atom in \(\mathrm{SiH}_{4}\) ? (b) To which point group does \(\mathrm{SiH}_{4}\) belong? (c) Sketch a qualitative MO diagram for the formation of \(\mathrm{SiH}_{4}\) from Si and an \(\mathrm{H}_{4}\) -fragment. Label all orbitals with appropriate symmetry labels.
