Problem 93
Write three reasonable resonance structures for the azide ion \(\mathrm{N}_{3}^{-}\) in which the atoms are arranged as NNN. Show formal charges.
Problem 94
Draw two resonance structures for sulfurous acid \(\left(\mathrm{H}_{2} \mathrm{SO}_{3}\right):\) one that obeys the octet rule for the central atom, and one that minimizes the formal charges. Determine the formal charge on each atom in both structures.
Problem 95
Give an example of an ion or molecule containing \(\mathrm{Al}\) that (a) obeys the octet rule, (b) has an expanded octet, and (c) has an incomplete octet.
Problem 96
Draw four reasonable resonance structures for the \(\mathrm{PO}_{3} \mathrm{~F}^{2-}\) ion. The central \(\mathrm{P}\) atom is bonded to the three \(\mathrm{O}\) atoms and to the \(\mathrm{F}\) atom. Show formal charges.
Problem 97
Attempts to prepare the compounds \(\mathrm{CF}_{2}, \mathrm{LiO}_{2}, \mathrm{CsCl}_{2},\) and \(\mathrm{PI}_{5}\) as stable species under atmospheric conditions have failed. Suggest possible reasons for the failure.
Problem 98
Draw reasonable resonance structures for the following ions: (a) \(\mathrm{HSO}_{4}^{-},\) (b) \(\mathrm{PO}_{4}^{3-}\), (c) \(\mathrm{HPO}_{3}^{2-},(\mathrm{d}) \mathrm{IO}_{3}^{-}\)
Problem 99
Are the following statements true or false? (a) Formal eharges represent an actual separation of charges. (b) \(\Delta H_{\mathrm{rxn}}^{\circ}\) can be estimated from the bond enthalpies of reactants and products. (c) All second- period elements obey the octet rule in their compounds. (d) The resonance structures of a molecule can be separated from one another in the laboratory.
Problem 100
A rule for drawing plausible Lewis structures is that the central atom is generally less electronegative than the surrounding atoms. Explain why this is so.
Problem 101
Using the following information and the fact that the average \(\mathrm{C}-\mathrm{H}\) bond enthalpy is \(414 \mathrm{~kJ} / \mathrm{mol}\), estimate the standard enthalpy of formation of methane \(\left(\mathrm{CH}_{4}\right)\). $$ \begin{aligned} \mathrm{C}(s) & \longrightarrow \mathrm{C}(g) & & \Delta H_{\mathrm{rxn}}^{\circ}=716 \mathrm{~kJ} / \mathrm{mol} \\ 2 \mathrm{H}_{2}(g) & \longrightarrow & 4 \mathrm{H}(g) & \Delta H_{\mathrm{rxn}}^{\circ} &=872.8 \mathrm{~kJ} / \mathrm{mol} \end{aligned} $$
Problem 103
Which of the following molecules has the shortest nitrogen-to-nitrogen bond: \(\mathrm{N}_{2} \mathrm{H}_{4}, \mathrm{~N}_{2} \mathrm{O}, \mathrm{N}_{2}, \mathrm{~N}_{2} \mathrm{O}_{4} ?\) Explain.
