Chpt8 - Chapter 8 Concepts of Chemical Bonding Chemical...

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Chapter 8 Concepts of Chemical Bonding
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Chemical Bonds A bond is a strong attraction between two atoms or ions. Three basic types of bonds: Ionic Electrostatic attraction between oppositely charged ions Covalent Sharing of electrons, usually between nonmetallic elements Metallic Bonds between metal atoms
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Lewis Symbols Lewis symbols are representations of elements using their chemical symbols and dots to indicate valence electrons Each side of symbol holds up to two electrons Each side of the symbol are equivalent
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Ionic Bonding Ionic bonds form between metal cations and nonmetal anions Cations are formed by the loss of electron(s) Anions are formed by the gain of electron(s) Octet rule states that atoms tend to gain, lose, or share electrons until they are surrounded by eight valence electrons.
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Ionic Bonding Metals have low ionization energies (want to give away electron) Nonmetals have high electron affinity (want to gain electron) After electron transfer both ions have an octet of electrons
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Energetics of Ionic Bonding As we saw in the last chapter, it takes 495 kJ/mol to remove electrons from sodium.
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Energetics of Ionic Bonding We get 349 kJ/mol back by giving electrons to chlorine.
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Energetics of Ionic Bonding But these numbers don’t explain why the reaction of sodium metal and chlorine gas to form sodium chloride is so exothermic! Na( s ) + ½Cl 2 ( g ) → NaCl( s ) ΔH o f = −410.9 kJ
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Energetics of Ionic Bonding There must be other pieces to the puzzle The electrostatic attraction between the newly formed sodium cation and chloride anion
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Lattice Energy This third major piece of the puzzle is the lattice energy: The energy required to completely separate a mole of a solid ionic compound into its gaseous ions. The energy associated with electrostatic interactions is governed by Coulomb’s law:
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Lattice Energy Lattice energy, then, increases with the charge on the ions And lattice energy increases with decreasing size of ions.
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Energetics of Ionic Bonding By accounting for all of the energies (ionization energy, electron affinity, lattice energy, and enthapies of formation), we can get a good idea of the energetics involved in such a process.
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Energetics of Ionic Bonding This energy diagram also helps explain the “octet rule.” Metals, for instance, tend to stop losing electrons once they attain a noble gas configuration because energy would be expended that cannot be overcome by lattice energies.
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Covalent Bonding In these bonds atoms share electrons to achieve noble gas
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Chpt8 - Chapter 8 Concepts of Chemical Bonding Chemical...

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