Chapter 6

The connections in \(\mathrm{CH}_{3} \mathrm{NO}_{2}\) are: (a) Put in the remaining valence electrons to complete the Lewis dot diagram. (b) Using lines, solid wedges, and dashed wedges, draw the three-dimensional shape of this molecule. Indicate the numeric value of all bond angles.

Up until now, you've been drawing first a Lewis dot diagram (two-dimensional, shows lone electron pairs) and then a separate diagram showing molecule shape (three-dimensional, no lone pairs shown). Now begin combining the two, drawing one structure showing both threedimensional shape and all lone pairs. Draw such a structure for each of the following polyatomic ions. Name each shape, and indicate whether the ion has an overall dipole moment. If so, draw the dipole moment vector. (Hint: It's a good idea to continue to draw a regular Iewis diagram first, even though you do not show it in your final answer.) (a) \(\mathrm{CN}^{-}\) (b) \(\mathrm{ClO}_{4}^{-}\) (c) \(\mathrm{PCl}_{4}^{+}\) (d) \(\mathrm{NO}_{2}^{-}\)

Draw a combined Lewis dot, molecular-shape diagram for each of the following species. Name each shape, and indicate whether the molecule or ion has an overall dipole moment. If so, draw the dipole moment vector. (a) \(\mathrm{Cl}_{2} \mathrm{O}\) (b) NOF (c) \(\mathrm{PF}_{3}\) (d) \(\mathrm{ICl}_{2}^{+}\) (Hint: See problem statement and hint for Problem 6.69. Hint for \((b): \mathrm{N}=\mathrm{O}\) bonds are common.)

Draw a combined Lewis dot, molecular-shape diagram for each of the following species. Name each shape, and indicate whether the molecule or ion has a dipole moment. If so, draw the dipole moment vector. (Hint: See problem statement and hint for Problem 6.69.) (a) \(\mathrm{CHBr}_{3}\) (b) \(\mathrm{NF}_{3}\) (c) \(\mathrm{ClO}_{3}^{-}\) (d) \(\mathrm{CS}_{2}\)

Draw dot diagrams for the carbonate anion, \(\mathrm{CO}_{3}^{2-}\), and for the sulfite anion, \(\mathrm{SO}_{3}^{2-} .\) What is the electron-group configuration around the central atom in each anion? What is the molecular shape of each anion? Is either ion polar? If so, which one? Explain your choice.

Which, if any, of these molecules do you expect to be polar: \(\mathrm{CO}_{2}, \mathrm{CS}_{2}\), or \(\mathrm{CSO}\) (carbon is the central atom in all three molecules)? Explain your answer.

List the steps you take to decide (a) whether or not. a covalent bond is polar and (b) whether or not a molecule is polar.

Which should have the largest molecular dipole moment: \(\mathrm{H}_{2}, \mathrm{CO}_{2}, \mathrm{CH}_{3} \mathrm{~F}\), or \(\mathrm{CH}_{7} \mathrm{I}\) ?

What is the molecular shape of \(\mathrm{NCl}_{3}\) ? What is the electron-group geometry around \(\mathrm{N} ?\) Is this a polar molecule?

What is the difference between intermolecular forces and intramolecular forces? Which are stronger?

Although Lewis dot diagrams are useful in understanding how the valence electrons in a molecule are arranged, what important aspect of the molecule do they neglect to show?

Draw the three-dimensional shape of methanol, \(\mathrm{CH}_{3} \mathrm{OH}\). Indicate the numeric value of all bond angles. Is this molecule polar? If so, draw the molecular dipole moment vector.

Hydrogen peroxonitrite has the formula HNO_{s} with the atoms connected \(\mathrm{O}-\mathrm{N}-\mathrm{O}-\mathrm{O}-\mathrm{H}\). (a) Draw the dot diagram for this molecule. (b) Draw the three-dimensional shape of the molecule, showing the numeric value of all bond angles. (c) Describe the electron-group geometry and molecular shape around the \(\mathrm{N}\) and around each \(\mathrm{O}\) to the right of the \(\mathrm{N}\).

Explain the difference between electron-group geometry and molecular shape. How do you use electron-group geometry when deciding what shape a molecule has?

A student forgets that the \(\mathrm{N}\) in ammonia, \(\mathrm{NH}_{3}\) has a lone pair as well as its three single bonds. After checking Table \(6.2\), he mistakenly draws the molecule-three bonding groups, no lone pairsas having a trigonal planar shape. If the ammonia molecule really were trigonal planar, how would the intermolecular forces differ from what they actually are?

Under what conditions is the electron-group geometry for a molecule the same as the molecular shape?

What is the shape of the \(\mathrm{N}_{\hat{2}}^{-}\) anion? What is the numeric value of each bond angle in the anion?

Which should have the largest dipole moment: \(\mathrm{O}_{3}, \mathrm{H}_{2} \mathrm{O}\), or \(\mathrm{OF}_{2} ?\)

Covalent molecules that contain an \(\mathrm{O}-\mathrm{H}, \mathrm{N}-\mathrm{H}\), or \(\mathrm{F}-\mathrm{H}\) bond have very strong intermolecular forces. Explain why.

Draw each ion or molecule showing its threedimensional shape and valence electrons. For each species, name the electron-group geometry around the central atom (or atoms) and the molecular shape. Indicate whether each species has a molecular dipole moment. If so, draw the dipole moment vector. (a) \(\mathrm{NCCN}\) (b) \(\mathrm{BF}_{4}\) (c) \(\mathrm{NClO}_{2}\) (d) \(\mathrm{SeH}_{2}\)

White phosphorus, \(\mathrm{P}_{4}\), consists of four phosphorus atoms, with each atom bonded to the other three. Draw the three-dimensional shape of this molecule, showing all valence electrons and bond angles. (Hint: Begin by drawing one atom bonded to the three others using VSEPR theory, and then make the remaining connections.)

\(\mathrm{BH}_{3}\) and \(\mathrm{PH}_{3}\) each contain four atoms, with the three hydrogens surrounding the central atom. Do the two molecules have the same electron-group geometry? Do they have the same molecular shape? Name the geometry and the shape for both molecules. You know from Problem \(6.59\) that \(\mathrm{PH}_{3}\) is nonpolar. What about \(\mathrm{BH}_{3} ?\) Is it polar or nonpolar? Explain.

Some molecules have central atoms with steric numbers greater than 4 . For example, the central sulfur atom in \(\mathrm{SF}_{6}\) has a steric number of 6 . Its actual geometry (called octahedral), is shown below (all the bond angles are \(90^{\circ}\) or \(180^{\circ}\) ). (a) Are the bonds in \(\mathrm{SF}_{6}\) polar, polar covalent, or ionic? Explain. (b) Would you predict the \(\mathrm{SF}_{6}\) molecule to be polar or nonpolar? Justify your answer.

There are exceptions to the predictions of VSEPR. Consider \(\mathrm{CH}_{3}\), known as a methyl radical. (a) Create a dot diagram for the methyl radical. How is it fundamentally different from other dot diagrams you have done? (b) Use VSEPR to predict the shape of the methyl radical and draw it with that shape (treat the odd electron as a single electron group). (c) The methyl radical is known to be planar with \(120^{\circ} \mathrm{H}-\mathrm{C}-\mathrm{H}\) angles. What steric number is being employed here, and what is the carbon atom doing with respect to the odd electron in determining molecular shape? (d) The \(\mathrm{CF}_{3}\) radical does obey VSEPR. Draw it according to its VSEPR-predicted shape. What steric number is being employed here? (e) The \(\mathrm{C}-\mathrm{H}\) bond is shorter than the \(\mathrm{C}-\mathrm{F}\) bond. When bonds are short, the atoms at the ends of the bonds can bang into each other (this is called steric congestion) unless a geometry is adopted to get around this. Use this knowledge to explain why \(\mathrm{CH}_{3}\) violates VSEPR, but \(C F_{3}\) does not.

Given the electronegativities of \(\mathrm{F}\) and \(\mathrm{I}\), what would have to be true for \(\mathrm{IF}_{2}^{+}\) to be nonpolar? The fact that it is polar means what?

What is it about the trigonal bipyramidal shape that distinguishes it from all the other molecular shapes that we have covered? (Hint: Think about lone pairs of electrons.)

Consider the molecule \(\mathrm{BrCl}_{3}\). (a) Draw a dot diagram for the molecule. (b) Predict the molecule's electron group geometry. (c) Predict the molecule's shape (name the shape and draw it using wedges, lines, and broken lines, and indicate the ideal value of the bond angles). (d) Predict if the molecule is polar or nonpolar. If polar, draw the dipole moment for the molecule.

One student claims \(\mathrm{XeF}_{4}\) will be polar. Another claims it will be nonpolar. Which is right, and why?

Is CIFs polar or nonpolar? Fully explain your answer.