Inorganic: The Unit Cell

Unit 2

State

a physically uniform sample (density, flow, compressibility)

Phase

a chemically uniform sample (composition, structure)

London Forces

instantaneous dipoles (partial charges)

Dipole-dipole moment

permanent dipoles

Hydrogen Bonds

a particularly strong dipole (N, O, F)

Ion-dipole

ion is a full electrostatic charge

Ion-ion interactions

very strong networks formed

Crystalline

Well-ordered

Amorphous

Poorly ordered

Cubic Closest

ABC ABC ABC

Hexagonal Closest Packed

AB AB AB AB

Unit Cell

The smallest repeat unit in a 3-D lattice
Used to represent the entire lattice

Atom in body

1

Atom on edge

1/4

Atom on corner

1/8

Atom on face

1/2

Primitive Cubic

Body Centered Cubic 2 - atoms

Face Centered Cubic (closest packed) - 4 atoms

Alloys

Compounds of ≥2 metallic elements

Metals have low________ hold electrons loosely

Zeff

Non-metals have high __________, hold electrons tightly

Zeff

In order to conduct, the valence electron orbitals must ________

overlap

the valence electrons are held very ___________due to the electropositive nature of metals

weakly

Metals with more electrons in __________ orbitals conduct better

valence

Diamond stucture

Half are filled in ½ of Td holes

Other half are in usual CCP formation

Conductor

band overlap

Semiconductor

no band overlap

Valence band

bonding orbital band

Conducting band

antibonding orbital band

Band gap

Energy gap between Fermi level and bottom of
conduction band

Intrinsic Semiconductor

Electrons are promoted: valence band to conduction band thermally

Conductivity increases with….

temperature

Extrinsic Semiconducting

Small, controlled amount of impurity introduced (doping)

N-type semiconduction

P has one extra electron, which lies in a higher energy orbital
and can become delocalized with very small energy input

P-type semiconduction

Al has one fewer electron, creating electron “holes”
that become delocalized with very small energy input

P-n Junction

One way gate for e- flow (diode)

Transistor

npn or pnp

Polarization does what

Provides transition between covalent and ionic spectrum

octahedral holes

Tetrahedral holes in fcc

ratio of Td to Oh

2: 1

Rock salt

Cesium Chloride

Zinc Blende

Fluorite

Wurtzite

Antifluorite

Madelung Constant

Energy between a single ion and every other ion in specific lattice pattern

(attractive or repulsive)

Born constant

Nuclei can’t be too close together w/o repulsion

• ion

Large charges produce ________ lattice energies and ______ water solubilities

large; lower

Packing is ______ when ion sizes don’t match well, ________ solubility

poor; increases

Schottky Defect

Frankel Defect

Substitition Defect

F-centers

What kind of solids are F-centers most likely to occur in?

Simple salts (NaCl)

Perovskites

Common mineral structure finding applications in superconductors, pizoelectronics, solar cells

True/False: you might need more than one cell to accurately represent a perovskite.

True

What holes are filled in Rock Salt (cation)?

All octahedral holes (both exchange off)

What holes are filled in Zinc Blende (cation)

Half of tetrahedral

What cation holes are filled in Wurtzite?

Half of tetrahedral

What holes are filled in ANION for Fluorite?

All tetrahedral

What cation holes are filled for anti-fluorite?

All tetrahedral holes

Holes filled in CsCl

Like BCC, One in middle (cation)?

CsCl formula

MX

Rock salt formula

MX

Zinc Blende formula

MX

Wurtzite Formula

MX

Fluorite Formula

MX₂

Anti-fluorite formula

M₂X

How many nearest neighbors for unary ccp/hcp?

12

How many nearest neighbors for unary bcc?

8

CsCl Anion/Cation CN (NN)

Anion: 8

Cation: 8

Rock Salt nearest Neighbors

Anion: 6

Cation: 6

Zinc Blende Nearest neighbors

Anion: 4

Cation: 4

Wurtzite Nearest Neighbors

Anion: 4

Cation: 4

Fluorite Nearest Neighbors

Anion: 4

Cation: 8

Antifluorite Nearest Neighbors

Anion: 8

Cation: 4