Tinh thể

Solids
crystalline
amorphous
well defined structures
no orderly structure
glass
quartz
SiO2
crystal lattice
system of points
describes 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
1/8
x 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 g
mol
1 mol
6.022 x 1023 atoms
4 atoms
unit 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 cm
1 cm
1 x 10-2 m
1 x 10-12 m
1 pm
= 127 pm
r+2r+r
lattice parameter, a
X-Ray Diffraction by Crystals
Bragg Equation
n = 2d sin
diffraction
interference between waves caused by
object in their path
constructive or destructive

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 solids
atoms in lattice
carbon
sp3
sp2
sp2
hardest material known
conduct electricity -  e-
diamond
doesn’t conduct electricity
graphite
buckminsterfullerene
Covalent solids
atoms in lattice
metals
every lattice point -
atom of 1 metal
body-centered cubic
face-centered cubic
hexagonal close packed
brass
substitutional alloy
steel
interstitial alloy
share valence e-
e- “sea”
melting point
Na
97oC
Cr
1890oC
good conductors
Ionic Solids
trigonal hole
tetrahedral hole
octahedral hole
too small
r = 0.225 R
r = 0.414 R
composed of charged species –
anions and cations
each unit cell -
anions at lattice points
cations in “holes”
NaCl
face-centered cubic
CsCl
simple cubic
unit cell neutral
stoichiometry of compound
different in size
Molecular Solids
molecules in lattice
hemoglobin
reaction center
1988
1962
Perutz and Kendrew
Deisenhofer, Huber and Michel