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Factors affecting metallic bond strength Metallic crystal structures Factors affecting metallic bond strength: 1. Atomic (metallic) radius 2. No. of valence electrons Decrease Increase Na 371K K 336K Rb 312K Mg 922K Al 933K Melting Point (K) Open Structure (1 Type) Close-packed Structure (2 types) Open Structure: Body-centered cubic Co-ordination number: 8 Number of atom in a unit cell: 1 + 8 ( 1/8) = 2 Unit Cell Open Structure: Body-centered cubic Examples: Close-Packed Structure: Hexagonal close-packed abababab….. Co-ordination number: 12 (6 in its own layer, 3 in the layer above and 3 below.) hexagonal Close-Packed Structure: Hexagonal close-packed Example: Close-Packed Structure: Cubic close-packed abcabcab….. Co-ordination number: 12 (6 in its own layer, 3 in the layer above and 3 below.) also called face-centered cubic Close-Packed Structure: Cubic close-packed Examples: Tetrahedral hole Octahedral hole
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