159_fall_07_chapt_12_partial_suppl

159_fall_07_chapt_12_partial_suppl - Ch 12 1 Chapter 12...

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Unformatted text preview: Ch 12 1 Chapter 12 Intermolecular Forces: Liquids, Solids, and Phase Changes Ch 12 2 Intermolecular Forces: Liquids, Solids, and Phase Changes 12.3 Types of Intermolecular Forces 12.4 Properties of the Liquid State 12.5 The Uniqueness of Water 12.6 (Only bottom page 380 - 3) Bonding in Solids: Molecular Orbital Band Theory (Limited Material Covered) Ch 12 3 In this section we will discuss two models of bonding in solids: 1.Simple Qualitative Model The Electron-Sea Model of Metallic Bonding 2. Quantitative Molecular Orbital Band Theory Bonding in Solids pp. 380-3 Ch 12 4 Bonding in Solids - MO Band Theory – applied to Lithium metal • MO band theory is more quantitative than the “sea” of mobile delocalized valence electrons discussed in Chapter 9 for metals • Li atoms contain four valence orbitals, one 2s and three 2p. • When two lithium atoms combine (Li 2 ), their AOs form eight MOs within a certain range of energy • Four Li atoms (Li 4 ) form 16 MOs • A mole of Li atoms forms 4N A MOs (N A = Avogadro’s number). Ch 12 5 MO Band Theory - applied to Lithium- Continued • The orbital energies are so close together that they form a continuous band • The valence electrons enter the lower energy portion (valence band), while the higher energy portion (conduction band) remains empty. In lithium (and other metals), the valence and conduction bands have no gap between them • The band model proposes that the lower energy MOs are occupied by the valence electrons and make up the valence band • The empty MOs that are higher in energy make up the conduction band Ch 12 6 Figure 12.35 p. 381 The band of molecular orbitals in lithium metal. Ch 12 7 Figure 12.36 p.382 Electrical conductivity in a conductor, semiconductor, and insulator. Conductor (metal) Semiconductor (metalloid) Electrons can jump the small gap with heat Insulator (non- metal) The valence and conduction bands are contiguous in etals which means electrons can jump from the filled valence band to the unfilled conduction band if they receive an infinitesimally small quantity of energy.- Molecular Orbital Band Theory Most nonmetals, e’s cannot jump the large energy gap. Ch 12 8 Typical Exam Problem 35 Which of the following best describes the band gap in conductors and in insulators? conductor insulator AB. no band gap no band gap AC. no band gap small band gap AD. no band gap large band gap AE. small band gap no band gap BC. small band gap small band gap BD. small band gap large band gap BE. large band gap no band gap CD. large band gap small band gap CE. large band gap large band gap Ch 12 9 Effect of Temperature on Conductivity onductor (metal) hen the temp is increased, greater random otion of the atoms hinders electron ovement, which decreases the conductivity of a metal Semiconductor (metalloid) When the temp is increased, thermally excited electrons can cross the gap, which increases the conductivity of the metalloid Insulators (non-metals) When the temp is increased, the gap...
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This note was uploaded on 04/03/2008 for the course CHEM 159-160 taught by Professor Zbaida during the Fall '07 term at Rutgers.

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159_fall_07_chapt_12_partial_suppl - Ch 12 1 Chapter 12...

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