Chapter 7

(a) Name the strongest intermolecular force in \(\mathrm{CH}_{3} \mathrm{OH}, \mathrm{CH}_{3} \mathrm{Cl}, \mathrm{CH}_{3} \mathrm{CH}_{3}\), and \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (b) Rank these molecules from lowest to highest boiling point.

Show how two \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\) molecules in the liquid phase are oriented with respect to each other and explain why the molecules align this way.

Name the strongest intermolecular force expected in (a) Boron trifluoride, \(\mathrm{BF}_{3}\) (b) 1-Propanol, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) (c) Xenon, Xe (d) Hydrogen fluoride, HF (e) Hydrogen iodide, HI

Name the strongest intermolecular force expected in (a) Boron trifluoride, \(\mathrm{BF}_{3}\) (b) 1-Propanol, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) (c) Xenon, Xe (d) Hydrogen fluoride, HF (e) Hydrogen iodide, \(\mathrm{HI}\)

Which of the following do you expect to be nonmolecular solids? (a) Sodium hydroxide, \(\mathrm{NaOH}\) (b) Solid ethanol, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (c) Iron, Fe (d) Solid silane, \(\mathrm{SiH}_{4}\)

\(\mathrm{SiO}_{2}\), the main component of glass, is a solid at room temperature, and \(\mathrm{CO}_{2}\) is a gas at room temperature. How do the structures of these compounds explain this fact?

Arrange these substances in order of increasing melting point: \(\mathrm{CH}_{3} \mathrm{OH}, \mathrm{SiO}_{2}, \mathrm{C}_{2} \mathrm{H}_{6}, \mathrm{NaCl}\).

Ethylene glycol, \(\mathrm{CH}_{2} \mathrm{OHCH}_{2} \mathrm{OH}\), and pentane, \(\mathrm{C}_{5} \mathrm{H}_{12}\), have approximately the same molar mass. Nevertheless, one of these compounds boils at \(198{ }^{\circ} \mathrm{C}\), and the other boils at \(36{ }^{\circ} \mathrm{C}\). Which compound boils at which temperature? Use an argument based on intermolecular forces to justify your choice.

Sketch the hydrogen bonds present in the liquid 1-propanol, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\).

Both diamond and graphite are network solids consist solely of carbon atoms: In diamond, every carbon atom is bonded to four other carbon atoms. In graphite, every carbon atom is bonded to three other carbon atoms, creating sheets of atoms that lie on top of one another. (a) Which type of intermolecular forces exist between the sheets of carbon atoms in graphite? (b) Diamond is an extremely hard substance, whereas graphite is a soft, slippery substance often used as a lubricant. Use intramolecular and intermolecular forces to explain this difference in physical properties.

When considering which is stronger, a covalent bond or an ionic bond, why is it fairer to contrast the melting points of diamond and \(\mathrm{NaCl}\) than to contrast the melting points of ice and \(\mathrm{NaCl}\) ?

Metallic bonding is often described as a lattice of metal cations in a sea of valence electrons. What is it about metallic bonding that allows it to be described in this fashion?

Eicosane, \(\mathrm{C}_{20} \mathrm{H}_{42}\), has a higher melting point and a higher boiling point than water, even though water has hydrogen bonds between molecules and eicosane does not. Explain how this can be.

Most covalent molecular substances have much lower melting points than ionic substances. What does this say about the strength of a covalent bond relative to the strength of an ionic bond? Explain your answer.

Arrange in order of increasing boiling point: \(\mathrm{CO}_{2}, \mathrm{SO}_{2}, \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}, \mathrm{Al}\)

Shown below are the structures for two isomers of hydroxy-benzaldehyde. Structure (a) is 2-hydroxy-benzaldehyde and structure (b) is 4 -hydroxy- benzaldehyde. The melting point for isomer (a), \(2{ }^{\circ} \mathrm{C}\), is significantly lower than the melting point of isomer (b), \(118^{\circ} \mathrm{C}\). Based on your knowledge of intermolecular forces, suggest a substantive reason for this difference in melting points. (Hint: Consider the intermolecular forces that must be overcome to melt each compound and postulate a reason for the difference in the strengths of those forces).

Some bacteria have evolved in such a way to render the antibiotic Vancomycin ineffective. How did they accomplish this (make sure to explain the role of intermolecular forces)?