Chapter 10

Draw the Lewis structure for each organic compound from its condensed structural formula. a. \(\mathrm{C}_{2} \mathrm{II}_{4}\) b. \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) c. HCHO d. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) e. HCOOH

Use Lewis structures to explain why \(\mathrm{Br}_{3}^{-}\) and \(\mathrm{I}_{3}^{-}\) are stable, while \(\mathrm{F}_{3}{\underline{\phantom{xx}}}^{-}\) is not.

Use Lewis structures to explain why \(\mathrm{Br}_{3}{\underline{\phantom{xx}}}^{-}\) and \(\mathrm{I}_{3}{\underline{\phantom{xx}}}^{-}\) are stable, while \(F_{3}-\) is not.

Draw the Lewis structure for urea, \(\mathrm{H}_{2} \mathrm{NCONH}_{2}\), one of the compounds responsible for the smell of urine. (The central carbon atom is bonded to both nitrogen atoms and to the oxygcn atom.) Does urea contain polar bonds? Which bond in urea is most polar?

Some theories of aging suggest that free radicals cause certain diseases and perhaps aging in general. As you know from the Lewis model, such molecules are not chemically stable and will quickly react with other molecules. According to certain theories, free radicals may attack molecules within the cell, such as DNA, changing them and causing cancer or other diseases.

Free radicals are important in many environmentally significant reactions (see the Chemistry in the Emironment box on free radicals in this chapter). For example, photochemical smogsmog that results from the action of sunlight on air pollutants-forms in part by these two steps: \(\mathrm{NO}_{2} \stackrel{\mathrm{UV} \mathrm{Lgh}}{\longrightarrow} \mathrm{NO}+\mathrm{O}\) \(\mathrm{O}+\mathrm{O}_{2} \longrightarrow \mathrm{O}_{3}\)

The azide lon, \(\mathrm{N}_{3}\), is a symmetrical ion, all of whose contributing resonance structures have formal charges. Draw three important contributing structures for this ion.

The standard state of phosphorus at \(25^{\circ} \mathrm{C}\) is \(\mathrm{P}_{4}\). This molecule has four equivalent \(\mathrm{P}\) atoms, no double or triple bonds, and no expanded octets. Draw its Lewis structure.

Find the oxidation number of each sulfur in the molecule \(\mathrm{H}_{2} \mathrm{~S}_{4}\) which has a linear arrangement of its atoms.

Which statement is true of an endothermic reaction? a. Strong bonds break and weak bonds form. b. Weak bonds break and strong bonds form. c. The bonds that break and those that form are of approximately the same strength.

When a firecracker explodes, energy is obviously released. The compounds in the firecracker can be viewed as being "energy rich." What does this mean? Explain the source of the energy in terms of chemical bonds.

A fundamental difference between compounds containing ionic bonds and those containing covalent bonds is the existence of molecules. Fiplain why molecules exist in solid covalent compounds but not in solid ionic compounds.

In the very first chapter of this book, we described the scientific approach and put a special emphasis on scientific models or theories. In this chapter, we looked carefully at a model for chemical bonding (the Lewis model). Why is this theory successful? What are some of the limitations of the theory?

Draw the Lewis dot symbols for the atoms Al and O. Use the Lewis model to determine the formula for the compound formed from these two atoms.

Draft a list of step-by-step instructions for writing the correct Lewis dot structure for any molecule or polyatomic ion.

Pass a piece of paper around the group and ask each group member in turn to perform the next step in the process of determining a correct l.ewis structure (including formal charges on all atoms and resonance structures, if appropriate) for the following molecules and ions: \(\mathrm{N}_{2} \mathrm{H}_{4}, \mathrm{CCl}_{4}, \mathrm{CO}_{3}^{2-},\) and \(\mathrm{NH}_{4}^{+}\)