Chapter 4

Chlorine Bleach Chlorine combines with oxygen in several proportions. Dichlorine monoxide \(\left(\mathrm{Cl}_{2} \mathrm{O}\right)\) is used in the manufacture of bleaching agents. Potassium chlorate \(\left(\mathrm{KClO}_{3}\right)\) is used in oxygen generators aboard aircraft. Draw the Lewis structures for \(\mathrm{Cl}_{2} \mathrm{O}\) and \(\mathrm{ClO}_{3}^{-}\).

Methanol is a toxic alcohol with the molecular formula \(\mathrm{CH}_{4} \mathrm{O} .\) Draw the Lewis structure for methanol.

Carbon disulfide, \(\mathrm{CS}_{2},\) is a flammable, low-boiling liquid. Draw the Lewis structure for \(\mathrm{CS}_{2}.\)

Explain the concept of resonance.

How does resonance influence the stability of a molecule or an ion?

What factors determine whether or not a molecule or ion exhibits resonance?

What structural features do all the resonance forms of a molecule or ion have in common?

Explain why \(\mathrm{NO}_{2}\) is more likely to exhibit resonance than \(\mathrm{CO}_{2}.\)

Three equivalent resonance structures can be drawn for a nitrate ion. How much of the time does the bonding in a nitrate ion match any one of them?

Draw two Lewis structures showing the resonance that occurs in cyclobutadiene (C\(_{4} \mathrm{H}_{4}\) ), a cyclic molecule with a structure that includes a ring of four carbon atoms.

Pyridine \(\left(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{N}\right)\) and pyrazine \(\left(\mathrm{C}_{4} \mathrm{H}_{4} \mathrm{N}_{2}\right)\) have structures similar to benzene. Both compounds have structures with six atoms in a ring. Draw Lewis structures for pyridine and pyrazine showing all resonance forms. The N atoms in pyrazine are across the ring from each other.

Oxygen and nitrogen combine to form a variety of nitrogen oxides, including the following two unstable compounds that each have two nitrogen atoms per molecule: \(\mathrm{N}_{2} \mathrm{O}_{2}\) and \(\mathrm{N}_{2} \mathrm{O}_{3} .\) Draw Lewis structures for the molecules and show all resonance forms.

Oxygen and sulfur combine to form a variety of different sulfur oxides. Some are stable molecules and some, including \(\mathrm{S}_{2} \mathrm{O}_{2}\) and \(\mathrm{S}_{2} \mathrm{O}_{3},\) decompose when they are heated. Draw Lewis structures for these two compounds and show all resonance forms.

Draw Lewis structures for fulminic acid (HCNO) that show all resonance forms.

Draw Lewis structures for hydrazoic acid (HN \(_{3}\) ) that show all resonance forms.

Draw Lewis structures that show the resonance that occurs in dinitrogen pentoxide. (Hint: \(\mathrm{N}_{2} \mathrm{O}_{5}\) has an \(\mathrm{O}\) atom at its center.

Bacteria Make Nitrites Nitrogen-fixing bacteria convert urea \(\left[\mathrm{H}_{2} \mathrm{NC}(\mathrm{O}) \mathrm{NH}_{2}\right]\) into nitrite ions. Draw Lewis structures for the two species. Include all resonance forms. (Hint: There is a \(\mathrm{C}=\mathrm{O}\) bond in urea.)

How does the nitrogen-oxygen bond length in the nitrate ion compare to the nitrogen-oxygen bond length in the nitrite ion?

Why is the oxygen-oxygen bond length in \(\mathrm{O}_{3}\) different than the one in \(\mathrm{O}_{2} ?\)

Explain why the nitrogen-oxygen bond lengths in \(\mathrm{N}_{2} \mathrm{O}_{4}\) (which has a nitrogen-nitrogen bond) and \(\mathrm{N}_{2} \mathrm{O}\) are nearly identical ( 118 and 119 pm, respectively).

Do you expect the sulfur-oxygen bond lengths in sulfite \(\left(\mathrm{SO}_{3}^{2-}\right)\) and sulfate \(\left(\mathrm{SO}_{4}^{2-}\right)\) ions to be about the same? Why?

Rank the following ions in order of increasing nitrogenoxygen bond lengths: \(\mathrm{NO}_{2}^{-}, \mathrm{NO}^{+},\) and \(\mathrm{NO}_{3}^{-}.\)

Rank the following substances in order of increasing carbon-oxygen bond energy: \(\mathrm{CO}, \mathrm{CO}_{2},\) and \(\mathrm{CO}_{3}^{2-}.\)

Which has the longer carbon-carbon bond: acetylene \(\left(\mathrm{C}_{2} \mathrm{H}_{2}\right)\) or ethane \(\left(\mathrm{C}_{2} \mathrm{H}_{6}\right) ?\)

Which has the stronger carbon-carbon bond: acetylene \(\left(\mathrm{C}_{2} \mathrm{H}_{2}\right)\) or ethane \(\left(\mathrm{C}_{2} \mathrm{H}_{6}\right) ?\)

How can we use electronegativity to predict whether a bond between two atoms is likely to be covalent or ionic?

How are trends in electronegativity related to trends in atomic size?

Is the element with the most valence electrons in a row of the periodic table also the most electronegative?

What is meant by the term polar covalent bond?

Why are the electrons in bonds between different elements not shared equally?

Which of the following bonds are polar? $\mathrm{C}-\mathrm{Se}, \mathrm{C}-\mathrm{O}\( \)\mathrm{Cl}-\mathrm{Cl}, \mathrm{O}=\mathrm{O}, \mathrm{N}-\mathrm{H}, \mathrm{C}-\mathrm{H} .$ In the bond or bonds that you selected, which atom has the greater electronegativity?

Which of the binary compounds formed by the following pairs of elements contain polar covalent bonds, and which are considered ionic compounds? a. \(C\) and \(S\) b. Al and Cl c. Cand O d. Ca and O

Which of the beryllium halides, if any, are considered ionic compounds?

Describe how formal charges are used to choose between possible molecular structures.

How do the electronegativities of elements influence the selection of which Lewis structure is favored?

In a molecule containing \(S\) and \(O\) atoms, is a structure with a negative formal charge on sulfur more likely to contribute to bonding than an alternative structure with a negative formal charge on oxygen?

In a cation containing \(\mathrm{N}\) and \(\mathrm{O},\) why do Lewis structures with a positive formal charge on nitrogen contribute more to the actual bonding in the molecule than those structures with a positive formal charge on oxygen?

Hydrogen isocyanide (HNC) has the same elemental composition as hydrogen cyanide (HCN), but the H in HNC is bonded to the nitrogen atom. Draw a Lewis structure for HNC, and assign formal charges to each atom. How do the formal charges on the atoms differ in the Lewis structures for HCN and HNC?

Origins of Life The discovery of polyatomic organic molecules such as cyanamide (H \(_{2} \mathrm{NCN}\) ) in interstellar space has led some scientists to believe that the molecules from which life began on Earth may have come from space. Draw Lewis structures for cyanamide and select the preferred structure on the basis of formal charges.

Nitrogen is the central atom in molecules of nitrous oxide \(\left(\mathrm{N}_{2} \mathrm{O}\right) .\) Draw Lewis structures for another possible arrangement: \(\mathrm{N}-\mathrm{O}-\mathrm{N} .\) Assign formal charges and suggest a reason why the structure is not likely to be stable.

Use formal charges to determine which resonance form of each of the following ions is preferred: \(\mathrm{CNO}^{-}, \mathrm{NCO}^{-},\) and \(\mathrm{CON}^{-}.\)

Are all odd-electron molecules exceptions to the octet rule?

Describe the factors that contribute to the stability of structures in which the central atoms have more than eight valence electrons.

Why do \(\mathrm{C}, \mathrm{N}, \mathrm{O},\) and \(\mathrm{F}\) atoms in covalently bonded molecules and ions have no more than eight valence electrons?

Do atoms in rows 3 and below always have expanded valence shells? Explain your answer.

In which of the following molecules does the sulfur atom have an expanded valence shell? (a) \(\mathrm{SF}_{6} ;\) (b) \(\mathrm{SF}_{5} ;\) (c) \(\mathrm{SF}_{4}\) (d) \(\mathrm{SF}_{2}\)

In which of the following molecules does the phosphorus atom have an expanded valence shell? (a) \(\mathrm{POCl}_{3} ;\) (b) \(\mathrm{PF}_{5}\) (c) \(\left.\mathrm{PF}_{3} ; \text { (d) } \mathrm{P}_{2} \mathrm{F}_{4} \text { (which has a } \mathrm{P}-\mathrm{P} \text { bond }\right)\)

How many electrons are there in the covalent bonds surrounding the sulfur atom in the following species? (a) \(\mathrm{SF}_{4} \mathrm{O} ;\) (b) \(\mathrm{SOF}_{2} ;(\mathrm{c}) \mathrm{SO}_{3} ;(\mathrm{d}) \mathrm{SF}_{5}{-}.\)

How many electrons are there in the covalent bonds surrounding the phosphorus atom in the following species? (a) \(\mathrm{POCl}_{3} ;\) (b) \(\mathrm{H}_{3} \mathrm{PO}_{4} ;\) (c) \(\mathrm{H}_{3} \mathrm{PO}_{3} ;\) (d) \(\mathrm{PF}_{6}-.\)

Draw the Lewis structures of \(\mathrm{NOF}_{3}\) and \(\mathrm{POF}_{3}\) in which the group 15 element is the central atom and the other atoms are bonded to it. What differences are there in the types of bonding in the molecules?