1. Previously in
Chem 104:
examples of molecular solids
Born Haber Cycles
“why doesn’t that solid exist”
phase diagrams
TODAY
Interchapter of Modern Materials
Band Theory
and some Big Ideas in the chapter
Friday –
14.1, 14.2 & bring your questions for Recitation!

2. Metals have Bonding “Bands”
Big Idea 1.
Metals have Bonding “Bands”

3. How Band Theory Evolves from Molecular Orbital Theory
Recall the most basic view of MOT
Energy
antibonding orbital
atomic orbital,
Like 1s
atomic orbital,
Like 1s
bonding orbital

4. Make a little more complex:
Energy
2 antibonding MO’s
2 a.o.’s
2 a.o.’s
2 bonding MO’s

5. Make a lot more complex:
Energy
20 antibonding MO’s
20 a.o.’s
20 a.o.’s
20 bonding MO’s

6. Make a mole of a metal M: Energy
6.022 x 1023 MO.’s: a Band of Bonding MO’s
6.022 x 1023 MO.’s: a Band of
AntiBonding MO’s
6.022 x M a.o.’s:
make a Band
of many, many
closely spaced
Atomic orbitals
6.022 x 1023 a.o.’s

7. The Type of Element Determines Band Gap,
Band Gap = the energy separation between Bonding
and Antibonding Bands
Energy
AntiBonding
Band
Of a
Metal
Band Gap ~ 0 eV
Bonding
Band
Of a
Metal

8. The Type of Element Determines Band Gap
Energy
AntiBonding
Band
Of a
Metal
AntiBonding
Band
Of a
Network Solid
Band Gap is Large
Band Gap ~ 0 eV
Bonding
Band
Of a
Metal
Bonding
Band
Of a
Network Solid

9. ~0 Band Gap Allows Electronic Movement  makes Metal a Conductor
Energy
AntiBonding
Band
of a
Metal
is Empty
Conduction
Band
Valence e- e- e- e- e-
Band Gap ~ 0 eV e- e- e- e-
Bonding
Band
of a
Metal
is e- filled

10. Large Band Gap Prevents Electronic Movement  makes Metal an Insulator
Energy
Conduction Band
at High Energy
Band Gap is Too Large
for Electrons to “jump”
Valence
Band
At Low Energy

11. ~Small Band Gap Allows Electronic Movement if
Energy added  makes a Semiconductor
Energy
Conduction
Band e-
by E = Light: Solar Cells e-
Band Gap overcome e-
by E = Heat: Thermisters
(heat regulators)
Valence
Band

12. Big Idea 3.
Impurities Create New Possibilties

13. ~Impurities Decrease Band Gap  makes a Better Semiconductor
Energy
Conduction
Band Ge
Ga doped –
a p-type
semiconductor e- Ge
Valence
Band Ge

14. ~Impurities Decrease Band Gap  makes a Better Semiconductor
Energy
Conduction
Band Ge
As doped –
an n-type
semiconductor e- e- Ge
Valence
Band Ge

15. Combining a P-type and N-type Semiconductors Makes a Diode
Current  this way only

16. A Diode made of the right materials causes DE loss to be converted to Light: Light Emitting Diode (LED)
N-type
P-type e- e- e-

17. The funny thing about corundum is, when you have it in a clean single crystal, you get something much different.
Sapphire is Gem-quality corundum Al2O3
with Ti(4+) & Fe(2+) replacing Al(3+)

18. Ruby
Gem-quality corundum Al2O3
with ~3% Cr(3+) replacing Al(3+)

19. Al2O3
Corundum
Al(3+): CN=6, Oh
O(2-): CN=4, Td
Nothing
recognizable here..

20. Ceramics go beyond Dirt
Big Idea 4.
Ceramics go beyond Dirt

21. Ceramics: can mean many things Ceramics: The Traditional View
Make from ground up rocks (“dirt”)
Composition: MAlxSiyOz.H2O
from silicate and aluminosilicate minerals
Begin “Plastic” (workable, malleable) when mixed with water
HEAT causes vitrification (“glassification”)
Structure: Amorphous with polycrystallites
or vitreous (glass)
Properties: very high melting points—refractories (furnace linings)
brittle (not malleable)
high mechanical strength and stability
chemically inert

22. Common example and how they differ: Terra cotta -
Stoneware-
Porcelain -
China –
From “common” clay; red color from
FeO iron oxides in “dirt”
Fired at lowest temp; not glassy
From “common” clay;
Fired at higher temp
From flint + feldspar clays;
Fired at highest temp; more vitreous
Most translucent, most vitreous, most white, most pure
Clay (kaolin) from China: Al2O3.2SiO2.2H2O .
“Bone China” originally made from calcined bone, CaO
The ‘ring’ test…
Firing process: evaporates remaining water away
and initiates vitrification

23. What goes on top of Ceramics Is ceramic too — Glazes
Composition similar: silicates + flint + feldspar
(SiO2 + SiAlO3)
+ “flux” (K2O, ZnO, BaCO3
Structure: vitreous
Color from Transition Metal minerals/salts added
Fe(3+) – red-brown
Cu(2+) – turquoise blue and green
Co(2+) – “cobalt” blue
Ni(2+) – green, brown
Mn(2+) –purple, brown

24. Ceramics: the Modern View
Advanced Ceramics or Materials:
silicon carbides SiC and nitrides Si3N
composites: SiC/Al2O3 “whiskers”
Improved Properties:
tougher, higher temperatures, fewer defects
Examples from Dr. Lukacs
golf heads
Machine parts
tiles
All common stuff

25. Better materials for Solar cells
Biggest Idea 5.
New Materials are Hot
Snazzy graphite relatives: fullerenes, carbon nantubes
drug delivery??
electronics?
Better materials for Solar cells
Biomineralization: how does it grow like that?
Superconducting solids
Molecular Magnets
Artificial bone?