factors affecting metallic bond strength metallic crystal structures
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Factors affecting metallic bond strength
Metallic crystal structures
Factors affecting metallic bond strength:
1. Atomic (metallic) radius
Na Mg Al
371K 922K 933K
K
336K Melting
Rb Point (K)
312K
2. No. of valence electrons
Decrease in radius
Increase
In radius
Metallic bondingis 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 bondingFactors 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.
Metallic bonding10.4 Metallic crystals
Close-packed structure
Open structure
74 % of space occupied by atoms / co-ordination no. = 12
68 % of space occupied by atoms/ co-ordination no. = 8
Hexagonal close packed structure:“abab”
Cubic close-packed structure:”abcabc”
Body center cubic structure
Open Structure(1 Type)
Close-packed Structure(2 types)
Unit CellUnit Cell
Co-ordination Co-ordination number: number: 88
Number of atom Number of atom in a unit cell: in a unit cell:
1 + 8 ( 1/8)1 + 8 ( 1/8)= 2= 2
Open Structure:
Body-centered Body-centered cubiccubic
10.4 Metallic crystalsOpen structure
Open Structure:
Body-centered Body-centered cubiccubic
Examples:Examples:
Close-Packed Structure:
Hexagonal Hexagonal close-packedclose-packed
abababab…..
hexagonal
Co-ordination Co-ordination number: number: 1212(6 in its own layer, 3 (6 in its own layer, 3 in the layer above in the layer above and 3 below.)and 3 below.)
Hexagonal close-packed structure:“abab”
10.4 Metallic crystals
co-ordination no. = 12
Close-Packed Structure:
Hexagonal Hexagonal close-packedclose-packed
Example:Example:
Close-Packed Structure:
CubicCubicclose-packedclose-packed
abcabcab…..
Co-ordination Co-ordination number: number: 1212
(6 in its own layer, 3 (6 in its own layer, 3 in the layer above in the layer above and 3 below.)and 3 below.)
also called face-centered cubic
Cubic close-packed structure:”abcabc”
co-ordination no. = 12
10.4 Metallic crystals
Close-Packed Structure:
CubicCubicclose-packedclose-packed
Examples:Examples:
“abab” and “abcabc”
10.4 Metallic crystals
Tetrahedral hole
Octahedral hole
10.4 Metallic crystals