Problem 1
State what you understand by each of the following: (a) covalent radius, (b) bond dissociation enthalpy and (c) the standard enthalpy of atomization of an element.
Problem 4
(a) In an X-ray diffraction experiment, what causes the diffraction of the electromagnetic radiation? (b) Explain why X-ray diffraction results give a value of \(103 \mathrm{pm}\) for the length of a localized 2 -centre 2-electron terminal B-H bond in the \(\left[\mathrm{B}_{2} \mathrm{H}_{7}\right]^{-}\) ion (4.25) while the same bond is found to be \(118 \mathrm{pm}\) in length from the results of a neutron diffraction experiment.
Problem 13
By considering only valence electrons in each case, draw Lewis structures for the following molecules: (a) methane \(\left(\mathrm{CH}_{4}\right)\); (b) bromomethane \(\left(\mathrm{CH}_{3} \mathrm{Br}\right)\), (c) ethane \(\left(\mathrm{C}_{2} \mathrm{H}_{6}\right) ;\) (d) ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} ,\mathrm{OH}\right)\); (e) ethene \(\left(\mathrm{C}_{2} \mathrm{H}_{4}\right)\).
Problem 14
Draw Lewis structures for (a) \(\mathrm{F}_{2},(\mathrm{b}) \mathrm{Br}_{2},(\mathrm{c}) \mathrm{BrF}\) (d) \(\operatorname{Br} F_{3}\) and (e) \(\mathrm{BrF}_{5}\).
Problem 15
How many Lewis structures can you draw for \(\mathrm{C}_{2}\) ? In the text, we considered only one structure; suggest why the other structure(s) that you have drawn is (are) unreasonable. [Hint: Think about the distribution of the bonding electrons in space.]
Problem 17
Construct a complete MO diagram for the formation of \(\mathrm{Li}_{2}\) showing the involvement of both the core and valence electrons of the two lithium atoms. Determine the bond order in \(\mathrm{Li}_{2}\). Does the inclusion of the core electrons affect the value of the bond order?
Problem 21
The bond dissociation enthalpy of \(\mathrm{Na}_{2}\) is \(74 \mathrm{kJ} \mathrm{mol}^{-1}\). Do you expect the bond enthalpy in \(\left[\mathrm{Na}_{2}\right]^{+}\) to be less than, equal to or greater than \(74 \mathrm{kJ} \mathrm{mol}^{-1} ?\) Rationalize your answer.
Problem 23
Comment on the following observations. (a) An \(\mathrm{O}-\mathrm{O}\) bond is weaker than an \(\mathrm{S}-\mathrm{S}\) bond, but \(\mathrm{O}=\mathrm{O}\) is stronger than \(\mathrm{S}=\mathrm{S}\) (see Table 4.5 ). (b) There is evidence for an unstable \(\mathrm{Be}_{2}\) species with a bond enthalpy of \(10 \mathrm{kJ} \mathrm{mol}^{-1}\) and bond distance of \(245 \mathrm{pm}\) (c) \(P \equiv P\) bonds are weaker than \(N \equiv N\) or \(C \equiv C,\) but stronger than \(\mathrm{As} \equiv \mathrm{As}\) (d) The covalent radius for \(P\) appropriate for a triple bond is \(94 \mathrm{pm},\) but in \(\mathrm{P}_{4},\) the \(\mathrm{P}-\mathrm{P}\) bond distances are \(221 \mathrm{pm}\)
