40-41 MPropLandscape - Electrical ! ! ! ! ! Good conductors...

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CHEM 112 LRSVDS Material Properties 1 Electrical Good conductors of heat & electricity Create semiconductors Oxides are basic ionic solids Aqueous cations (positive charge, Lewis acids) Reactivity increases downwards in family Mechanical Lustrous (reflect light) Most are solids (which one is not?) Malleable (hammer into thin sheets) Ductile (drawn out into wires) Defects/Hardening affect strength Mixtures are Alloys CHEM 112 LRSVDS Material Properties 2 Free Electron Model What kind of interactions hold metal atoms together? How does this explain high electrical and thermal conductivity ? How does this explain malleability and ductility ?
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CHEM 112 LRSVDS Material Properties 3 As strength of metallic bond increases, What happens to the melting point? Electron Sea model cannot explain: ! BP, MP trends ! Heat of fusion ! Hardness of metals W Mo Cr CHEM 112 LRSVDS Material Properties 4 • Atomic orbitals (AOs) mix to form _____ • Start with 2 AOs, end with ____ MOs • Start with n AOs, end up with ____ MOs • In metals energy difference between orbitals in valence band is small. • MOs form a continuous “band” of allowed energy states .
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CHEM 112 LRSVDS Material Properties 5 CHEM 112 LRSVDS Material Properties 6 Most METALS are Conductors Band is partially filled by Valence electrons Some materials are Insulators or Semiconductors Valence band is full (or completely empty ). ! To conduct electricity, e - needs to be able to get to an empty orbital
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7 Insulators • Some elements (diamond, sulfur) • Many Ionic Solids • Network Covalent Solids • Organic Compounds (polymers) • Ceramics – inorganic, nonmetallic solids – can be covalent network and/or ionic bonded Examples: Aluminates (Al 2 O 3 ) Carbides (SiC, Ca 2 C) Oxides (BeO, ZrO 2 , Al 2 O 3 ) Nitrides (BN) Silicates (SiO 2 /metal oxides) CHEM 112 LRSVDS Material Properties 8 Silicon; essential to integrated circuits in computers, electronic devices Properties: shiny, silvery gray brittle Poor thermal conductor SEMI-METAL Uses: alloy (with Al, Mg) Silicone polymers Electronic applications for these applications very pure silicon (<1ppb) is required. Zone refining to get pure Si
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This note was uploaded on 01/18/2012 for the course CHEM 112 taught by Professor Vandersluys,lorschmid,kylem during the Fall '07 term at Pennsylvania State University, University Park.

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40-41 MPropLandscape - Electrical ! ! ! ! ! Good conductors...

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