11. Bonding & Molecular Structure

Which of the following is false?

Using Lewis symbols and Lewis structures, diagram the formation of BF3 from B and F atoms, showing valence-shell electrons. (e) Does BF3 obey the octet rule?

Draw Lewis structures for the following: (c) AsF5

(b) Which of these compounds or ions is an exception to the octet rule: borohydride (BH4-), borazine (B3N3H6, which is analogous to benzene with alternating B and N in the ring), or boron trichloride

Draw the Lewis structures for each of the following molecules or ions. Identify instances where the octet rule is not obeyed; state which atom in each compound does not follow the octet rule; and state how many electrons surround these atoms: (a) PF6-, (b) BeCl2, (c) NH3, (d) XeF2O (the Xe is the central atom), (e) SO42 - .

Write the Lewis structure for each molecule (octet rule not followed). a. BBr3 b. NO c. ClO2

Write Lewis structures for each molecule or ion. Use expanded octets as necessary. a. PF5

Consider the following XF4 ions: PF4-, BrF4-, ClF4+, and AlF4-. (a) Which of the ions have more than an octet of electrons around the central atom?

Although I3- is a known ion, F3- is not. (c) Another classmate says F3- does not exist because it would violate the octet rule. Is this classmate possibly correct?

Use Lewis structures to explain why Br3- and I3- are stable, while F3- is not.

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 may also attack molecules on the surfaces of cells, making them appear foreign to the body's immune system. The immune system then attacks the cells and destroys them, weakening the body. Draw Lewis structures for each free radical implicated in this theory of aging. c. OH

Free radicals are important in many environmentally significant reactions (see the Chemistry in the Environment box on free radicals in this chapter). For example, photochemical smog— smog that results from the action of sunlight on air pollutants— forms in part by these two steps: NO2 UV light NO + O O + O2 O3 The product of this reaction, ozone, is a pollutant in the lower atmosphere. (Upper atmospheric ozone is a natural part of the atmosphere that protects life on Earth from ultraviolet light.) Ozone is an eye and lung irritant and also accelerates the weathering of rubber products. Rewrite the given reactions using the Lewis structure of each reactant and product. Identify the free radicals.