Chapter-8-KW - Chapter 8 Chemical Bonding: General Concepts...

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Chapter 8 Chemical Bonding: General Concepts
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Index 8.1 Electron transfer leads to the formation of ionic compounds 8.2 Lewis symbols help keep track of valence electrons 8.3 Covalent bonds are formed by electron sharing 8.4 Covalent bonds can have partial charges at opposite ends 8.5 The reactivities of metals and nonmetals can be related to their electronegativities 8.6 Drawing Lewis structures is a necessary skill 8.7 Resonance applies when a single Lewis structure fails
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8.1 Electron transfer leads to the formation of ionic compounds 3 Lattice Energy Compound Ions Lattice Energy (kJ mol−1) LiCl Li+ and Cl− 845 NaCl Na+ and Cl− 787 KCl K+ and Cl− 709 LiF Li+ and F− 1033 CaCl2 Ca2+ and Cl− 2258 AlCl3 Al3+ and Cl− 5492 CaO Ca2+ and O2- 3401 Al2O3 Al3+ and O2- 15,916 Formation of gaseous ions from an ionic solid AxBy( s )→xBy+( g ) + yBx-( g )
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8.1 Electron transfer leads to the formation of ionic compounds 4 Born Haber Cycle for NaCl 2Na( s ) + Cl2( g ) → 2NaCl( s ) What has to happen? Sublime Na: Δ H sub = 107.8 kJ/mol Break Cl bond: ½( DCl-Cl) = 121.3 kJ/mol Ionize Na: IE = 495.4 kJ/mol Ionize Cl: EA = -348.8 kJ/mol Form bond: Lattice Energy = -787 kJ/mol
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8.1 Electron transfer leads to the formation of ionic compounds 5 Lattice Energy and Bond Formation Energy The formation of one mole of solid from gaseous ions ( ionic bond formation ) is numerically the same as the lattice energy Na+( g ) + Cl-( g ) → NaCl( s ) + 787 kJ Since this is energy released, the value for this process would be the lattice energy Smaller ions have greater attractive forces, as have those with higher charges § q 1 and q 2 are charges on the particles § k is a proportionality constant § r is the distance between the two ions 2 1 Lattice Energy = q q kr
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8.1 Electron transfer leads to the formation of ionic compounds 6 Electron Configurations Ions 1. The first electrons to be lost by an atom or ion are always those from the shell with the largest value of n 2. As electrons are removed from a given shell, they come from the highest-energy occupied subshell first before any are removed from a lower-energy subshell. 3. Within a given shell, the energies of the subshells vary as follows: s p d f .
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8.1 Electron transfer leads to the formation of ionic compounds 7 Electron Configurations of Cations Main Group metals lose the electrons in their highest energy subshell first to achieve the previously filled noble gas (the octet rule ) Group IA: [Noble gas core]n s 1 § Form 1+ ions to be isoelectronic with noble gas core element Group IIA: [Noble gas core]n s 2 § Forms 2+ ions Group IIIA: [Noble gas core]n s 2n p 1 § Forms 3+ ions
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8.1 Electron transfer leads to the formation of ionic compounds 8 Electron Configuration of Cations Main Group metals lose the electrons in their highest energy subshell first. Elements in group IIIA below Al also form 1+ ions.
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Chapter-8-KW - Chapter 8 Chemical Bonding: General Concepts...

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