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22 Chemistry of the Nonmetals Solutions to Exercises (c) The anion that is the strongest base in water is the conjugate base of the weakest conjugate acid. The conjugate acids are OH-, SH⁻, and According to trends in binary hydrides, the acid with the longest X-H bond will be the most readily ionized and the strongest acid. is thus the strongest acid and OH- the weakest. Therefore is the strongest base in water. 22.8 Analyze/Plan. Evaluate the graph, describe the trend in data, recall the general trend for each of the properties listed, and use details of the data to discriminate between possibilities. Solve. The general trend is an increase in value moving from left to right across the period, with a small discontinuity at S. Considering just this overall feature, both (a) first ionization energy and (c) electronegativity increase moving from left to right, so these are possibilities. (b) Atomic radius decreases, and can be eliminated. Since Si is a solid and Cl and Ar are gases at room temperature, melting points must decrease across the row; (d) melting point can be eliminated. According to data in Tables 22.2, 22.5, 22.7, and 22.8, (e) X-X single bond enthalpies show no consistent trend. Furthermore, there is no known Ar-Ar single bond, so no value for this property can be known; (e) can be eliminated. Now let's examine trends in (a) first ionization energy and (c) electronegativity more closely. From electronegativity values in Chapter 8, we see a continuous increase with no discontinuity at S, and no value for Ar. Values in (a) first ionization energy from Chapter 7 do match the pattern in the figure. The slightly lower value of I₁ for S is due to a decrease in repulsion by removing an electron from a fully occupied orbital. In summary, only (a) first ionization energy fits the property depicted in the graph. 22.9 The compound on the left, with the strained three-membered ring, will be the most generally reactive. For central atoms with four electron domains*, idealized bond angles are 109°. From left to right, the bond angles in the three molecules pictured are 60°, 90° and 108 The larger the deviation from ideal bond angles, the more strain in the molecule and the more generally reactive it is. *For the stick structures shown in the exercise, each line represents a C-C single bond and the intersection of two lines is a C atom. To determine the number of electron domains about each atom, visualize or draw the hydrogen atoms and nonbonded electron pairs in each molecule. Alternatively, note that both C and atoms form only single bonds, so hybridization must be sp³ and idealized bond angles are 109°. 22.10 Analyze/Plan. The structure shown is a diatomic molecule or ion, depending on the value of n. Each species has 10 valence electrons and 5 electron pairs. Solve. (a) Only second row elements are possible, because of the small covalent radius required for multiple bonding. Likely candidates are CO, N₂, NO+, and :NEN: (b) Since has the highest negative charge, it is likely to be the strongest acceptor and strongest Bronsted base. This is confirmed in Section 22.9 under "Carbides." 671