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:
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.
Solution 104 E Step 1 of 7 Radicals are those species having high reactivity because they have an ood number of electrons, thus one of them will be surely unpaired. Thus, one of the molecule’s atoms will have an incomplete valence shell. Step 2 of 7 Explain The NO m2ecule We have N in central position and O to its sides The total electrons are calculated by using this formula Total electron= Valence electrons in N) + 2(Valence electrons in O)= 5 + 2(6)= 5+12=17 Since we have an odd number of electrons, we can just guess there will be an unpaired electron, in fact, after giving the bonding pairs and lone pairs to each atom, we obtain this molecular structure. Step 3 of 7 Explain The NO molecule We have N in central position and an atom of O next to it The total electrons are calculated by this formula Total electron= (Valence electrons in N) + (Valence electrons in O)= 5 + 6= 5=11 Even in this case we have an odd number of electrons, so we can just guess there will be an unpaired electron. In fact, after giving the bonding pairs and lone pairs to each atom, we obtain this molecular structure. Step 4 of 7 Explain the O atom We have the atom of O with six electrons. Oxygen respects its number of electrons of valence, moreover it has an even number of electrons so, although it hasn’t a complete valence shell, this specie is not a radical