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Chapter 23 Chemistry of the Nonmetals 497 23.19 Because OH has charge, Al has a +3 charge, and Si₂O₅ has a -2 charge, OX state) + 1(Si₂O₅ charge) + x charge) = 0; so 2(+3) + 1(-2) + x(-1) = 0 and x = 4. 23.21 In Table 23.2, has a -4 charge and it belongs to the class of orthosilicates, where the silicate tetrahedra stand alone, not linked to each other. The -4 charge balances with a common oxidation state of Zr of +4. 23.23 Ca has a +2 charge, Mg has a +2 charge, Fe commonly has a charge of +2 or +3, and OH has a charge of -1. So far, the charge balance is 2(+2) + 4(+2) + or +3) + charge) +2(-1) = 0 or charge = - 12 or 13. Looking at Table 23.2 and recalling that one unit replaces one SiO₂ unit, units are the best match. If we double the unit and replace one-eighth of the Sis by Al, the new unit will be and the charge will be 2(-6) - 1 = 13. The charge on Fe will be +3, and the class is amphibole, with a double chain structure. Boron and Its Remarkable Structures 23.25 Given: Na₂ = kernite, 1.0 X 10³ kg of kernite-bearing ore, 0.98% by mass kernite, 65% recovery Find: g boron recovered Conceptual Plan: kg ore g ore g kernite g B possible g B recovered 1000 g 0.98 g kernite 4(10.81) g B 65 g B recovered 1 kg 100 g ore Solution: 291.30 g kernite 100gB 1.0 X 1000 1 kgore X 0.98 100 X 291.30 kernite X 65 g 100 B recovered = 950 g B recovered Check: The units (g) are correct. The magnitude of the answer makes physical sense because there is very little mineral in the ore, a low recovery, and little B in the ore. 23.27 The bond angles are different in BCl₃ versus NCl₃ because B has three valence electrons and N has five valence electrons. The boron compound does not obey the octet rule: B has sp² hybridization and a trigonal planar geometry. The nitrogen compound does obey the octet rule and has a lone pair of electrons, sp³ hybridization, and a trigonal pyramidal geometry (based on a tetrahedral geometry). 23.29 (a) Looking at Figure 23.11, B₆H₆²⁻ has six vertices and eight faces because it has an octahedral shape. (b) has the formula of a closo-borane and has 12 vertices and 20 faces because it has an icosahedral shape. 23.31 Closo-boranes have the formula BₙHₙ²⁻ and form fully closed polyhedra with triangular sides. Each of the vertices in the polyhedra is a boron atom with an attached hydrogen atom. Nido-boranes, named from the Latin word for net, have the formula They consist of a cage of boron atoms missing one corner. Arachno-boranes, named from the Greek word for web, have the formula They consist of a cage of boron atoms that is missing two or three corners. Carbon, Carbides, and Carbonates 23.33 Regular charcoal is in large chunks that still resemble the wood from which it is made. Activated charcoal is treated with steam to break up the chunks into a finely divided powder with a high surface area. 23.35 Ionic carbides are composed of carbon and low-electronegativity metals such as the alkali metals and alkaline earth metals. Most of the ionic carbides contain the dicarbide ion, commonly called the acetylide ion. Covalent car- bides are composed of carbon and low-electronegativity nonmetals or metalloids. The most important covalent carbide is silicon carbide (SiC), a very hard material. Copyright © 2017 Pearson Education, Inc.