Chemistry 18 Wednesday, October 11, 2006

Chemistry 18 Wednesday, October 11, 2006 - Wednesday,...

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Wednesday, October 11, 2006 Chemistry SOLID STRUCTURES How are ionic and covalent compounds arranged in the solid? What governs melting points? Text : Sections 8.7 – 8.8, 8.10 Element Covalent Compound Ionic Compound Metallic Solid Molecular solid “network” Covalent solid ionic solid (ex. cubic) Unit: Atom Molecule Atom ion Held Metallic bond dispersion covalent ionic By bond dipole-dipole bonds bond (bond th.) H-bonding (bond th.) IONIC SOLIDS 1. Held together by ionic bonds a. +/1 attraction 2. adopt structures such that + are surrounded by – a. usually anions larger than cations b. common motif: i. anions pack efficiently ii. cations fill void space FIGURE 8.12 3. “sodium chloride structure” a. Coord. # = 6 b. Poor for packing equalized spheres 4. CsCl adapts the “cesium chloride structure” a. Coord. # = 8 “NETWORK” COVALENT SOLIDS 1. all atoms held together by covalent bonds (intra and intermolecular) 2. Different from “molecular solids” a. There: weaker intermolecular. Forces allow one molecule to “stick” to another 3. Here: one molecule covalently bonded to another (much stronger)
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Chemistry 18 Wednesday, October 11, 2006 - Wednesday,...

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