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Energy of NaF vs. MgO solid formation

Energy of NaF vs. MgO solid formation - 6 I 0 CHAPTER I3...

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Unformatted text preview: 6 I 0 CHAPTER I3 Bonding: GeneraL Concepts M 2’1 )+0"(} 737-!— Electron affinity Mg“(3) + 0(3) 7 247 M3‘+(g} +‘l 02(3) —3 164— Lattice energy E 2180'“— Ionization energy + . Na+(g) + F(g) Na (8) + '2 PM!) —328 ‘— Electron 1 . Nahg) + F'tg) ”my 495 F Ionization I energy Mats} + '2 02(3) . Nata} + 3 Fats) Na(s) + s F ( ) —923 4...... Lattice ener Overall gy 2 ‘— energy—.- _570 change NaF(s) FIGURE I3." Comparison of the energy changes involved in the formation of solid sodium fluoride and solid magnesium oxide. Note the large lattice energy for magnesium oxide (where doubly charged ions are combining) compared with that for sodium fluoride (where singly charged ions are combining). of 2180 kjlmol) is much greater than the energy required to remove an electron from a sodium atom {495 kjlmol). Energy (737 kjl'mol) is required to add two electrons to the oxygen atom in the gas phase. Addition of the first electron is exothermic (— 141 kjr'mol), but addition of the second electron is quite endothermic (878 kjs’mol). This latter energy must be obtained indirectly, since the 02_{g) is not stable. Because twice as much energy is required to remove the second electron from magnesium as to remove the first, and because addition of an electron to the gaseous 0— ion is quite endothermic, it seems puzzling that magnesium oxide contains Mg2+ and 02' ions rather than Mg+ and 0— ions. The answer ...
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