Chapter 4

The phosphate ion \(\left(\mathrm{PO}_{4}^{3-}\right)\) is part of our DNA. The corresponding nitrogen-containing oxoanion, \(\mathrm{NO}_{4}^{3-},\) is not chemically stable. Draw Lewis structures that show any resonance forms of both oxoanions.

Dissolving NaF in selenium tetrafluoride (SeF \(_{4}\) ) produces NaSeF\(_{5}\), Draw the Lewis structures of \(\mathrm{SeF}_{4}\) and \(\mathrm{SeF}_{5}\). In which structure does Se have more than eight valence electrons?

The reaction between \(\mathrm{NF}_{3}, \mathrm{F}_{2},\) and \(\mathrm{SbF}_{3}\) at \(200^{\circ} \mathrm{C}\) and 100 atm pressure produces the ionic compound \(\mathrm{NF}_{4} \mathrm{SbF}_{6}\) Draw the Lewis structures of the ions in the product.

\(\mathrm{Cl}_{2} \mathrm{O}_{2}\) decomposes to \(\mathrm{Cl}_{2}\) and \(\mathrm{ClO}_{2} .\) Draw the Lewis structure of \(\mathrm{ClO}_{2}.\)

Which of the following chlorine oxides are odd-electron molecules? (a) \(\mathrm{Cl}_{2} \mathrm{O}_{7} ;\) (b) \(\mathrm{Cl}_{2} \mathrm{O}_{6} ;\) (c) \(\mathrm{ClO}_{4} ;\) (d) \(\mathrm{ClO}_{3}\) (e) \(\mathrm{ClO}_{2}\)

Which of the following nitrogen oxides are odd-electron molecules? (a) \(\mathrm{NO} ;\) (b) \(\mathrm{NO}_{2} ;\) (c) \(\mathrm{NO}_{3} ;\) (d) \(\mathrm{N}_{2} \mathrm{O}_{4} ;\) (e) \(\mathrm{N}_{2} \mathrm{O}_{5}.\)

In the following species, which atom is most likely to have an unpaired electron? (a) \(\mathrm{SO}^{+} ;\) (b) \(\mathrm{NO} ;\) (c) \(\mathrm{CN} ;\) (d) \(\mathrm{OH}.\)

Describe how atmospheric greenhouse gases act like the panes of glass in a greenhouse.

Water vapor in the atmosphere contributes more to the greenhouse effect than carbon dioxide, yet water vapor is not considered an important factor in climate change. Propose a reason why.

Increasing concentrations of nitrous oxide in the atmosphere may be contributing to climate change. Is the ability of \(\mathrm{N}_{2} \mathrm{O}\) to absorb IR radiation due to nitrogen-nitrogen bond stretching, nitrogen- oxygen bond stretching, or both? Explain your answer.

Is the ability of \(\mathrm{H}_{2} \mathrm{O}\) molecules to absorb photons of IR radiation due to symmetrical stretching or asymmetrical stretching of its \(\mathrm{O}-\mathrm{H}\) bonds, or both? Explain your answer. (Hint: The angle between the two O-H bonds in \(\left.\mathrm{H}_{2} \mathrm{O} \text { is } 104.5^{\circ} .\right).\)

Can molecules of carbon monoxide in the atmosphere absorb photons of IR radiation? Explain why or why not.

How does the high-temperature conversion of limestone \(\left(\mathrm{CaCO}_{3}\right)\) to lime (CaO) during the production of cement contribute to climate change?

Why does infrared radiation cause bonds to vibrate but not break (as UV radiation can)?

Argon is the third most abundant species in the atmosphere. Why isn't it a greenhouse gas?

Which \(\mathrm{C}-\) O bond has a higher stretching frequency: the one in CO or the one in \(\mathrm{CH}_{2} \mathrm{O}\) ? Explain your selection.

Which compound, NO or \(\mathrm{NO}_{2},\) absorbs IR radiation of a longer wavelength?

Use formal charges to predict whether the atoms in carbon disulfide are arranged CSS or SCS.

Use formal charges to predict whether the atoms in hypochlorous acid are arranged HOCl or HC1O.

Chemical Weapons Draw the Lewis structure of phosgene, \(\mathrm{COCl}_{2},\) a poisonous gas used in chemical warfare during World War I.

A compound with the formula \(\mathrm{Cl}_{2} \mathrm{O}_{6}\) decomposes to a mixture of \(\mathrm{ClO}_{2}\) and \(\mathrm{ClO}_{4} .\) Draw two Lewis structures for \(\mathrm{Cl}_{2} \mathrm{O}_{6}:\) one with a chlorine-chlorine bond and one with a \(\mathrm{Cl}-\mathrm{O}-\mathrm{Cl}\) arrangement of atoms.

The \(\mathrm{TeOF}_{6}^{2-}\) anion was first synthesized in \(1993 .\) Draw its Lewis structure.

Sulfur in the Environment Sulfur is cycled in the environment through compounds such as dimethyl sulfide \(\left(\mathrm{CH}_{3} \mathrm{SCH}_{3}\right),\) hydrogen sulfide \(\left(\mathrm{H}_{2} \mathrm{S}\right),\) and sulfite and sulfate ions. Draw Lewis structures for these four species. Are expanded valence shells needed to minimize the formal charges for any of these species?

Antacid Tablets Antacids commonly contain calcium carbonate and/or magnesium hydroxide. Draw the Lewis structures for calcium carbonate and magnesium hydroxide.

How many pairs of electrons does xenon share in the following molecules and ions? (a) \(\mathrm{XeF}_{2} ;\) (b) \(\mathrm{XeOF}_{2}\) (c) \(\mathrm{XeF}^{+} ;\) (d) \(\mathrm{XeF}_{5}^{+} ;\) (e) \(\mathrm{XeO}_{4}\)

A short-lived allotrope of nitrogen, \(\mathrm{N}_{4},\) was reported in 2002 a. Draw the Lewis structures of all the resonance forms of linear \(\mathrm{N}_{4}(\mathrm{N}-\mathrm{N}-\mathrm{N}-\mathrm{N}).\) b. Assign formal charges and determine which resonance structure is the best description of \(\mathbf{N}_{4}.\) c. Draw a Lewis structure of a ring (cyclic) form of \(\mathrm{N}_{4}\) and assign formal charges.

Scientists have predicted the existence of \(\mathrm{O}_{4},\) even though the molecule has never been observed. However, \(\mathrm{O}_{4}^{2-}\) has been detected. Draw the Lewis structures for \(\mathrm{O}_{4}\) and \(\mathrm{O}_{4}^{2-}.\)

Which of the following molecules and ions contains an atom with an expanded valence shell? (a) \(\mathrm{Cl}_{2} ;\) (b) \(\mathrm{ClF}_{3}\); (c) \(\mathrm{CII}_{3} ;\) (d) \(\mathrm{ClO}^{-}\)

Which of the following molecules contains an atom with an expanded valence shell? (a) \(\mathrm{XeF}_{2} ;\) (b) \(\mathrm{GaCl}_{3} ;\) (c) \(\mathrm{ONF}_{3}\);(d) \(\mathrm{SeO}_{2} \mathrm{F}_{2}\)

A linear nitrogen anion, \(\mathrm{N}_{5}\), was isolated for the first time in 1999. a. Draw the Lewis structures for four resonance forms of linear \(\mathrm{N}_{5}^{-}.\) b. Assign formal charges to the atoms in the structures in part (a), and identify the structures that contribute the most to the bonding in \(\mathrm{N}_{5}^{-}\). c. Compare the Lewis structures for \(\mathrm{N}_{5}^{-}\) and \(\mathrm{N}_{3}^{-}\). In which ion do the nitrogen-nitrogen bonds have the higher average bond order?

Plot the electronegativities of elements with \(Z=3\) to \(9(y \text { -axis) versus their first ionization energy ( } x\) -axis). Is the plot linear? Use your graph to predict the electronegativity of neon, whose first ionization energy is \(2081 \mathrm{kJ} / \mathrm{mol}.\)

In the typical Lewis structure of \(\mathrm{BF}_{3}\) there are only six valence electrons on the boron atom and each \(\mathrm{B}-\mathrm{F}\) bond is a single bond. However, the length and strength of these bonds indicate that they have a small measure of doublebond character-that is, their bond order is slightly greater than 1. a. Draw a Lewis structure of \(\mathrm{BF}_{3}\), including all resonance structures, in which there is one \(\mathrm{B}=\mathrm{F}\) double bond. b. What is the formal charge on the \(\mathrm{B}\) atom, and what is the average formal charge on each \(\mathrm{F}\) atom? c. Based on formal charges alone, what should be the bond order of each \(\mathrm{B}-\mathrm{F}\) bond in \(\mathrm{BF}_{3} ?\) d. What factor might support a bond order slightly greater than \(1 ?\)

The cation \(\mathrm{N}_{2} \mathrm{F}^{+}\) is isoelectronic with \(\mathrm{N}_{2} \mathrm{O}\). a. What does it mean to be isoelectronic? b. Draw the Lewis structure of \(\mathrm{N}_{2} \mathrm{F}^{+}\). (Hint: The molecule contains a nitrogen-nitrogen bond.) c. Which atom has the +1 formal charge in the structure you drew in part (b)? d. Does \(\mathrm{N}_{2} \mathrm{F}^{+}\) have resonance forms? e. Could the middle atom in the \(\mathrm{N}_{2} \mathrm{F}^{+}\) ion be a fluorine atom? Explain your answer.

Ozone Depletion Methyl bromide \(\left(\mathrm{CH}_{3} \mathrm{Br}\right)\) is produced naturally by fungi. Methyl bromide has also been used in agriculture as a fumigant, but its use is being phased out because the compound has been linked to ozone depletion in the upper atmosphere. a. Draw the Lewis structure of \(\mathrm{CH}_{3} \mathrm{Br}\). b. Which bond in \(\mathrm{CH}_{3} \mathrm{Br}\) is more polar, carbon-hydrogen or carbon-bromine?

Draw the Lewis structure for dimethyl ether, \(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}\), given that the structure contains an oxygen atom bonded to two carbons: \(\mathrm{C}-\mathrm{O}-\mathrm{C}.\)

Draw another Lewis structure for \(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}\) that has a different connectivity than that in Problem \(4.175 .\) (Hint: Remember that the bonding capacity of hydrogen is \(1 .\) )

Draw the Lewis structure for butane, \(\mathrm{C}_{4} \mathrm{H}_{10},\) given the structure contains four carbon atoms bonded in a row: \(\mathrm{C}-\mathrm{C}-\mathrm{C}-\mathrm{C}.\)