Lect3 Tinh thể
description
Transcript of Lect3 Tinh thể
Solids
crystalline
amorphous
well defined structures
no orderly structure glass
quartz
SiO2
crystal lattice system of pointsdescribes arrangement of particles
unit cell repeating structural unit lattice
7 unit cells
simple cubic
formed from packing spheres
unit cells
crystalline solids
hexagonal closest packing
“abab” layers “abca” layers
cubic packing
“aaa” layers
in 3 dimensions
hexagonal closest pack cubic closest pack
“abab” layers
simple cubic body centered cubic
Three-Dimensional Cubic Lattices
Simple cubic
Face-centered cubic
Body-centered cubic
1/8x 8 =1 particle
(1/8 )x 8 + 1 = 2 particles
(1/8 )x 8 (1/2 )x 6+ = 4 particles
cubic closest pack
a a a
a b a b
a b c a b c
coordination number = 6
coordination number = 8
coordination number = 12
Calculation of atomic radii
Cu faced-centered cubic
density = 8.92 g/cm3
mass = 63.546 g/mol
63.546 gmol
1 mol6.022 x 1023 atoms
4 atomsunit cell 8.92 g
cm3
4.732 x 10-23 cm3 / unit cell( )1/3
= 3.617 x 10-8 cm
(3.617 x 10-8)2 + (3.617 x 10-8)2 = (4r)2
r = 1.279 x 10-8 cm1 cm1 x 10-2 m
1 x 10-12 m1 pm = 127 pm
r+2r+r
lattice parameter, a
X-Ray Diffraction by Crystals
Bragg Equation n = 2d sin
diffraction interference between waves caused byobject in their pathconstructive or destructive
d
Types of Crystalline Solids
Covalent Ionic Molecular atoms in lattice ions in lattice molecules in lattice
m.p. depends on bonding forces
Cdiamond 3550oC NaCl 800OC H2O 0oC
covalent ionic H-bonding
Covalent solidsatoms in lattice
carbon
sp3 sp2 sp2
hardest material known conduct electricity - e-
diamond
doesn’t conduct electricity
graphite buckminsterfullerene
Covalent solidsatoms in lattice
metals every lattice point - atom of 1 metal
body-centered cubicface-centered cubichexagonal close packed
brass substitutional alloy
steel interstitial alloy
share valence e- e- “sea”
melting pointNa 97oCCr 1890oC
good conductors
Ionic Solids
trigonal hole tetrahedral hole octahedral holetoo small r = 0.225 R r = 0.414 R
composed of charged species –
anions and cationseach unit cell -
anions at lattice points cations in “holes”NaCl face-centered cubicCsCl simple cubic
unit cell neutralstoichiometry of compound
different in size
Molecular Solids molecules in lattice
hemoglobin reaction center
19881962Perutz and Kendrew Deisenhofer, Huber and Michel