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11.7 Metallic Bonding

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McGill University
CHEM 110
Ariel Fenster

October 27th 11.7 Metallic Bonding Material 10.9 and 11.8 not covered 40 multiple choice questions  5 Questions from Sanctuary and 35 new material Metal Properties:  Luster or reflectivity  High electrical conductivity  High thermal conductivity  Malleability and ductility  Electronic emission Key Features of Metals:  Few Valence electrons and many empty orbitals  Metals in crystals surrounded by many neighboring atoms, regular array of the nuclei  For instance, the Electron-Sea Model; electrons move freely among array of positive charges Coloumb’s Law: determines the Electron- Sea Model E = k Q1 Q2 / d Luster or Reflectivity:  Since electrons are not localized within a bond of a particular energy, they can absorb and emit light of all frequencies High Electrical Conductivity:  Since electrons are not localized within a bond, they are extremely mobile (they can hope and move)  Electricity comes in one side and hopes out the other (electron in, electron out) Clicker Question: Does electrical conductivity increase or decrease with increased temperature? Decreases, at higher temperatures, the increased vibration of the positive ions interferes with the motion of the electrons. By interfering with the electrons, the conductivity will decrease. High Thermal Conductivity:  Electrons can move easily, therefore electrons in hot regions migrate to cooler regions and transfer their energy to the crystal lattice  Relationship between thermal and electrical conductivity: strong relationship  those that are good thermal conductors are also good electrical conductors October 27 th 11.7 Metallic Bonding Malleability and Ductility:  Metals can bend; be made into a sheet (malleable)  Metals can be drawn into wire (ductile) y r r  Off set nuclei, and move them around, the electron sea can still cope E 2s E 2s with those changes  Metal becomes deformed, but still remains a metal  a offset of electrons (positive beside positive) Na Na Na2 g g e e E 2s E 2s Electronic Emission:  Since electrons are not localized within a bond, they are extremely mobile Na Na2 Na 3 Na Na2 Na3 Na4 Band Theory: METALLIC PROPERTIES  Atomic orbitals in metallic crystal mix to form bands of closely spaced metallic orbitals Luster or reflectivity  Example: Na High electrical conductivity Since electrons are not localized within a High thermal conductivity bond, they are extremely mobile Malleability & ductility Electronic emission Half-filled 2s valence band r r 2s n n ENERRGY BAND E 2s E Na Na2 Na 3 Na4 Nan Nan BAND THEORY BAND THEORY Atomic orbitals in metallic crystal mix to form bands of closely spaced metallic orbitals th October 27 11.7 Metallic Bonding Example: Mg Electrons are promoted to the p orbital  Forming a conduction 3p band. g g e e VALENCE BAND n n E 3s E 3p g g e e E 3s E Mg Mg 2 Mgn Mg Mg2 Mgn Three Possible Conductivities: CONDUCTION BAND CONDUCTION BAND CONDUCTION BANDn semi-conductors, the conductivity CONDUCTION BAND CONDUCTION BAND increases with temperatures. g g r y r g y CONDUCTION BAND g n
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