Factors affecting metallic bond strength Metallic crystal structures F.6 Metallic Bond Factors affecting metallic bond strength Metallic crystal structures

Factors affecting metallic bond strength: 1. Atomic (metallic) radius 2. No. of valence electrons Decrease in radius Na Mg Al 371K 922K 933K K 336K Melting Rb Point (K) 312K Increase In radius

Metallic bonding is an electrostatic attraction between sea of electrons and positive ions. Metallic radius: as half the internuclear distance between two atoms in a metallic crystal

Metallic bonding Factors affecting the strength of metallic bonding: 1. number of valence electrons (outermost electrons / bonding electrons) and charge on cations. e.g. b.p. : Al > Mg > Na 2. metallic radius. e.g. b.p. : Li > Na > K i.e. larger no. of valence electrons, smaller metallic radius will result in stronger metallic bonds.

Close-packed structure Open structure Metallic bonding 10.4 Metallic crystals Close-packed structure Open structure 68 % of space occupied by atoms/ co-ordination no. = 8 74 % of space occupied by atoms / co-ordination no. = 12 Hexagonal close packed structure:“abab” Cubic close-packed structure:”abcabc” Body center cubic structure

Close-packed Structure (2 types) Open Structure (1 Type) Close-packed Structure (2 types)

Unit Cell Co-ordination number: 8 Number of atom in a unit cell: Open Structure: Body-centered cubic Co-ordination number: 8 Number of atom in a unit cell: 1 + 8 ( 1/8) = 2 Unit Cell

10.4 Metallic crystals Open structure

Iron and all Group I metals Open Structure: Body-centered cubic Examples: Iron and all Group I metals

abababab….. hexagonal Co-ordination number: 12 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

10.4 Metallic crystals co-ordination no. = 12 Hexagonal close-packed structure:“abab”

Close-Packed Structure: Hexagonal close-packed Example: Magnesium

abcabcab….. also called face-centered cubic Co-ordination number: 12 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

10.4 Metallic crystals co-ordination no. = 12 Cubic close-packed structure:”abcabc”

Copper, Gold, Silver Examples: Close-Packed Structure: Cubic close-packed Examples: Copper, Gold, Silver

10.4 Metallic crystals “abab” and “abcabc”

Tetrahedral hole Octahedral hole

10.4 Metallic crystals