Chapter 5

Why is the shape of a molecule determined by repulsions between electron pairs and not by repulsions between nuclei?

In which molecular geometry do equatorial bonding pairs of electrons repel each other more: square pyramidal or trigonal bipyramidal?

Why do \(\mathrm{NO}_{3}^{-}\) and \(\mathrm{NO}_{2}^{-}\) ions have similar \(\mathrm{O}-\mathrm{N}-\mathrm{O}\) bond angles, even though they have different numbers of \(\mathrm{N}-\mathrm{O}\) bonds?

Why do \(\mathrm{CF}_{4}, \mathrm{SF}_{4},\) and \(\mathrm{XeF}_{4}\) have different molecular geometries, even though they all consist of a central atom bonded to four fluorine atoms?

Why are the bond angles in \(\mathrm{BH}_{3}\) and \(\mathrm{NH}_{3}\) different, even though they both consist of a central atom bonded to three hydrogen atoms?

The O-N-O bond angle in \(\mathrm{NO}_{2}^{+}\) is larger than it is in \(\mathrm{NO}_{2} .\) Why?

Why are the \(\mathrm{H}-\mathrm{C}-\mathrm{H}\) bond angles in molecules of \(\mathrm{CH}_{4}\) smaller than the \(\mathrm{H}-\mathrm{C}-\mathrm{H}\) bond angles in molecules of \(\mathrm{CH}_{2} \mathrm{O} ?\)

Why do we need to draw the Lewis structure of a molecule before predicting its geometry?

Why does the seesaw structure have lower energy than a trigonal pyramidal structure when \(\mathrm{SN}=5 ?\)

Do all resonance forms of a molecule have the same molecular geometry? Explain your answer.

Rank the following molecules in order of increasing bond angles: (a) \(\mathrm{NH}_{2} \mathrm{Cl} ;\) (b) \(\mathrm{CCl}_{4} ;\) (c) \(\mathrm{H}_{2} \mathrm{S}\)

Rank the following molecular geometries in order of increasing bond angles: (a) trigonal pyramidal; (b) trigonal planar; (c) square planar.

Which of the following electron-pair geometries is not consistent with a linear molecular geometry, assuming three atoms per molecule? (a) tetrahedral; (b) octahedral; (c) trigonal planar

How many lone pairs of electrons would there have to be on a \(\mathrm{SN}=6\) central atom for it to have a linear molecular geometry?

Determine the molecular geometries of the following molecules: (a) GeH \(_{4} ;\) (b) \(\mathrm{PH}_{3} ;\) (c) \(\mathrm{H}_{2} \mathrm{S} ;\) (d) \(\mathrm{CHCl}_{3}.\)

Determine the molecular geometries of the following molecules and ions: (a) \(\mathrm{NO}_{3}^{-} ;\) (b) \(\mathrm{NO}_{4}^{3-} ;\) (c) \(\mathrm{NCN}^{2-}\) (d) \(\mathrm{NF}_{3}.\)

Determine the molecular geometries of the following ions: (a) \(\mathrm{NH}_{4}^{+} ;\) (b) \(\mathrm{CO}_{3}^{2-} ;\) (c) \(\mathrm{NO}_{2}^{-} ;\) (d) \(\mathrm{XeF}_{5}^{+}.\)

Determine the molecular geometries of the following ions: (a) \(\mathrm{SCN}^{-} ;\) (b) \(\mathrm{CH}_{3} \mathrm{PCl}_{3}^{+}(\mathrm{P}\) is the central atom and is bonded to the \(\mathrm{C}\) atom of the methyl group); (c) \(\mathrm{ICl}_{2}^{-}\) (d) \(\mathrm{PO}_{3}^{3-}.\)

Determine the molecular geometries of the following ions: (a) \(\mathrm{S}_{2} \mathrm{O}_{3}^{2-} ;\) (b) \(\mathrm{PO}_{4}^{3-} ;\) (c) \(\mathrm{NO}_{3}^{-} ;\) (d) \(\mathrm{NCO}^{-}.\)

Determine the molecular geometries of the following molecules: (a) \(\mathrm{ClO}_{2} ;\) (b)\(\mathrm{ClO}_{3} ;(c) \mathrm{IF}_{3}\); (d) \(\mathrm{SF}_{4}\)

Which two of the triatomic molecules \(\mathrm{O}_{3}, \mathrm{SO}_{2},\) and \(\mathrm{CO}_{2}\) have the same molecular geometry?

Which two of the species \(\mathrm{N}_{3}^{-}, \mathrm{O}_{3},\) and \(\mathrm{CO}_{2}\) have the same molecular geometry?

Which two of the ions \(\mathrm{SCN}^{-}, \mathrm{CNO}^{-},\) and \(\mathrm{NO}_{2}^{-}\) have the same molecular geometry?

Which two of the molecules \(\mathrm{N}_{2} \mathrm{O}, \mathrm{Se}_{2} \mathrm{O},\) and \(\mathrm{CO}_{2}\) have the same molecular geometry?

For many years, it was believed that the noble gases could not form covalently bonded compounds. However, xenon does react with fluorine. One of the products is the pentafluoroxenate anion, \(\mathrm{XeF}_{5}^{-} .\) Draw the Lewis structure of \(\mathrm{XeF}_{5}^{-}\) and predict its geometry.

The first compound containing a xenon-sulfur bond was isolated in \(1998 .\) Draw a Lewis structure for HXeSH and determine its molecular geometry.

Determine the electron-pair geometries around the nitrogen atoms in the following unstable nitrogen oxides: (a) \(\mathrm{N}_{2} \mathrm{O}_{2}\) (b) \(\mathrm{N}_{2} \mathrm{O}_{5} ;\) (c) \(\mathrm{N}_{2} \mathrm{O}_{3}$$\left(\mathrm{N}_{2} \mathrm{O}_{2} \text { and } \mathrm{N}_{2} \mathrm{O}_{3} \text { have } \mathrm{N}-\mathrm{N}\right.\) bonds; \(\left.\mathrm{N}_{2} \mathrm{O}_{5} \text { does not. }\right)\)

Explain the difference between a polar bond and a polar molecule.

Must a polar molecule contain polar covalent bonds? Why?

Can a nonpolar molecule contain polar covalent bonds?

What does a dipole moment measure?

The following molecules contain polar covalent bonds. Which of them are polar molecules and which have no permanent dipoles? (a) \(\mathrm{CCl}_{4} ;\) (b) \(\mathrm{CHCl}_{3} ;\) (c) \(\mathrm{CO}_{2} ;\) (d) \(\mathrm{H}_{2} \mathrm{S}\) (e) \(\mathrm{SO}_{2}\)

Which of the following molecules has a permanent dipole? (a) \(\mathrm{C} \equiv \mathrm{O} ;\) (b) \(\mathrm{N} \equiv \mathrm{N} ;\) (c) \(\mathrm{H}-\mathrm{C} \equiv \mathrm{N} ;\) (d) \(\mathrm{H}-\mathrm{C} \equiv \mathrm{C}-\mathrm{H}.\)

Compounds containing carbon, chlorine, and fluorine are known as chlorofluorocarbons (CFCs). Which of the following CFCs are polar and which are nonpolar? (a) \(\mathrm{CFCl}_{3} ;\) (b) \(\mathrm{CF}_{2} \mathrm{Cl}_{2} ;\) (c) \(\mathrm{Cl}_{2} \mathrm{FCCF}_{2} \mathrm{Cl}.\)

Which of the following molecules has a permanent dipole? (a) \(\mathrm{C}_{4} \mathrm{F}_{8}\) (cyclic structure); (b) \(\mathrm{ClFCCF}_{2} ;\) (c) \(\mathrm{Cl}_{2} \mathrm{HCCClF}_{2}.\)

Predict which molecule in each of the following pairs is more polar: (a) \(\mathrm{CClF}_{3}\) or \(\mathrm{CBrF}_{3} ;\) (b) \(\mathrm{CF}_{2} \mathrm{Cl}_{2}\) or \(\mathrm{CHF}_{2} \mathrm{Cl}\).

Which molecule in each of the following pairs is more polar? (a) \(\mathrm{NH}_{3}\) or \(\mathrm{PH}_{3} ;\) (b) \(\mathrm{CCl}_{2} \mathrm{F}_{2}\) or \(\mathrm{CBr}_{2} \mathrm{F}_{2}.\)

A compound with the formula \(\mathrm{COCl}_{2}\) has been used as a chemical warfare agent. It and two similar compounds, \(\mathrm{COBr}_{2}\) and \(\mathrm{COI}_{2}\), are all eye irritants and cause skin to blister. The severity of the skin reactions is influenced by the polarity of the compounds. Rank the compounds in order of increasing polarity of their \(\mathrm{C}-\mathrm{X}\) bonds (where \(\mathrm{X}\) is a halogen atom).

What must atomic orbitals have in common to mix together and form hybrid orbitals?

Why do atomic orbitals form hybrid orbitals?

What is the hybridization of the underlined carbon atom in each of these condensed structural formulas? (a) \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{3} ;\) (b) \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{CH}_{3}\) (c) \(\mathrm{CH}_{3}-\mathrm{CH}\left(\mathrm{CH}_{3}\right)-\mathrm{CH}_{3} ;\) (d) \(\mathrm{CH} \equiv \mathrm{C}-\mathrm{CH}_{3}\) (e) \(\mathrm{CH} \equiv \mathrm{C}-\mathrm{CH}_{3}\)

What is the hybridization of nitrogen in each of the following ions and molecules? (a) \(\mathrm{NO}_{2}^{+} ;\) (b) \(\mathrm{NO}_{2}^{-} ;\) (c) \(\mathrm{N}_{2} \mathrm{O}\) (d) \(\mathrm{N}_{2} \mathrm{O}_{5} ;\) (e) \(\mathrm{N}_{2} \mathrm{O}_{3}.\)

Azides such as sodium azide, NaN \(_{3}\) are used in automobile air bags as a source of nitrogen gas. Another compound with three nitrogen atoms bonded together is \(\mathrm{N}_{3} \mathrm{F}\). What differences are there between the arrangements of the electrons around the nitrogen atoms in the azide ion \(\left(\mathrm{N}_{3}^{-}\right)\) and in \(\mathrm{N}_{3} \mathrm{F}\) ? Is there a difference in the hybridization of the central nitrogen atom?

How does the hybridization of the central atom change in the series \(\mathrm{CO}_{2}, \mathrm{NO}_{2}, \mathrm{O}_{3}, \mathrm{ClO}_{2} ?\)

How does the hybridization of the sulfur atom change in the series \(\mathrm{SF}_{2}, \mathrm{SF}_{4}, \mathrm{SF}_{6} ?\)

Health Perchlorate compounds adversely affect human health by interfering with the uptake of iodine in the thyroid gland. Because of that behavior, though, they are also used to treat hyperthyroidism, or overactive thyroid. Draw the Lewis structure(s) of the perchlorate ion, \(\mathrm{ClO}_{4}^{-}\), including all resonance forms, in which formal charges are closest to zero. What is the shape of the ion? Suggest a hybridization scheme for the central chlorine atom that accounts for this shape.

Draw the Lewis structure of the chlorite ion, \(\mathrm{ClO}_{2}^{-},\) which is used as a bleaching agent. Include all resonance structures in which formal charges are closest to zero. What is the shape of the ion? Suggest a hybridization scheme for the central chlorine atom that accounts for the structures you have drawn.

Synthesis of the first compound of argon was reported in 2000. HArF was made by reacting Ar with HF. Draw the Lewis structure for HArF and determine the hybridization of Ar in this molecule.

Draw a Lewis structure for \(\mathrm{Cl}_{3}^{+}\). Determine its molecular geometry and the hybridization of the central Cl atom.

Do all resonance forms of \(\mathrm{N}_{2} \mathrm{O}\) have the same hybridization at the central \(\mathrm{N}\) atom?