125ch11c(2) - Relationship between unit cell types atoms...

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Unformatted text preview: Relationship between unit cell types, # atoms, coordination no., packing efficiency edge length and particle radius sc # atoms/uc coord # % space occupied % empty space edge length in terms of radius 1 6 52 % 48 % l= 4r 4 bcc 2 8 68 % 32 % l= 4r 3 fcc (ccp) 4 12 74 % 26 % l= 4r 2 hcp X 12 74 % 26 % X 28a Table 13-10 Characteristics of Types of Solids Metallic Particles of unit cell Metal ions in "electron gas." Ionic Anions, cations Molecular Molecules (or atoms) Atoms Covalent Strongest interparticle forces Metallic bonds (attractions between cations and eG `s) Electrostatic London, dipole-dipole, and/or hydrogen bonds Covalent bonds Properties Soft to very hard; good thermal and electrical conductors; wide rage of melting points. (!39 to 3400C) Hard; brittle; poor thermal and electrical conductors; high melting points (400 to 3000C) Soft; poor thermal and electrical conductors; low melting points (!272 to 400C) Very hard; poor thermal and electrical conductors;* high melting points (1200 to 4000C) Examples Li, K, Ca, Cu, Cr, Ni (metals) NaCl, CaBr2, K2SO4 (typical salts) CH4 (methane), P4, O2, Ar, CO2, H2O, S8 C (diamond), SiO2 (quartz) mostly group 4A (C, Si, Ge, Gray Sn, SiC) and a few others (BN, GeO2) *Exceptions: diamond is a good conductor of heat; graphite is soft and conducts electricity well. Copyright Whitten, Davis & Peck, 5th edition, 1996 33 ...
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