Chapter 8 - Concepts of Chemical Bonding

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

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1 Chapter 8 Chapter 8 Concepts of Concepts of Chemical Bonding Chemical Bonding Chemical Bonds Chemical Bonds • Three basic types of bonds: –Ionic • Electrostatic attraction between ions –Covalent • Sharing of electrons –Metallic • Metal atoms bonded to several other atoms
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2 Energetics of Ionic Bonding Energetics of Ionic Bonding As we saw in the last chapter, it takes 495 kJ/mol to remove electrons from sodium. Energetics of Ionic Bonding Energetics of Ionic Bonding We get 349 kJ/mol back by giving electrons to chlorine.
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3 Energetics of Ionic Bonding 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! Energetics of Ionic Bonding Energetics of Ionic Bonding • There must be a third piece to the puzzle. • What is as yet unaccounted for is the electrostatic attraction between the newly formed sodium cation and chloride anion.
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4 Lattice Energy Lattice Energy • This third 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: E el = κ Q 1 Q 2 d Lattice Energy Lattice Energy • Lattice energy, then, increases with the charge on the ions. • It also increases with decreasing size of ions.
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5 Energetics of Ionic Bonding Energetics of Ionic Bonding By accounting for all three energies (ionization energy, electron affinity, and lattice energy), we can get a good idea of the energetics involved in such a process. Energetics of Ionic Bonding Energetics of Ionic Bonding •These phenomena 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
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Covalent Bonding Covalent Bonding • In these bonds atoms share electrons. • There are several electrostatic interactions in these bonds: – Attractions between electrons and nuclei – Repulsions between electrons – Repulsions between nuclei Polar Covalent Bonds Polar Covalent Bonds • Although atoms often form compounds by sharing electrons, the electrons are not always shared equally. • Fluorine pulls harder on the electrons it shares with hydrogen than hydrogen does. • Therefore, the fluorine end of the molecule
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This note was uploaded on 05/09/2010 for the course CHEMISTRY 3150:153 taught by Professor Hu,jun during the Spring '10 term at Kent State.

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

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