8: Chapter Solid Materials
Types of solids
C
C H2O SiO2 Ca(CO3)
Cu
Liquid Crystals
Structure of solids
crystalline Long range order X O X O O X O X X O X O O X O X X O X O O X O X X O X O O X O X amorphous Local order X O X X O X O X O X X X X X O O X O O X O X O X X O X X O X O O
Crystal lattice: pattern of the ordered array Unit cell: simplest portion that shows the pattern
Section 8.0
There are seven different types of unit cells
X-Ray Diffraction
Structure of solids Unit cell: simplest portion that shows the pattern (repeat unit) Cubic unit cells sc simple cubic bcc lattice sites fcc Body-centered corners Face-centered cubic cubic lattice sites lattice sites corners & center corners & faces
Section 8.1
simple cubic (primitive) lattice sites: corners Packing Efficiency = 52 % Very light material. Not dense. Example: Polonium Coordination Number = 6 Atoms/cell = 8 corner atoms x 1/8 ownership Atoms/cell = 1 Atom
Section 8.1-8.5
Body-centered cubic lattice sites : Corners & Center Packing Efficiency = 68 % More dense than SCC Example: iron Coordination Number = 8 Atoms/cell = 8 corner atoms x 1/8 ownership + 1 central atom at full ownership Atoms/cell = 2 Atoms
Section 8.1-8.5
Face-centered cubic lattice sites:Corners & Faces Packing Efficiency = 74 % Most Dense cubic cell Example: iron in stainless steel Coordination Number = 12 Atoms/cell = 8 corner atoms x 1/8 ownership + 6 face atoms x 1/2 ownership Atoms/cell = 4 Atoms
Section 8.1-8.5
Unit Cell Ownership of Atoms
A cube has 1 center It takes 1 cube to "contain" a center atom
1 center atom at full ownership = 1 atom
Section 8.3
Unit Cell Ownership of Atoms
A cube has 6 faces
It takes 2 cubes to "contain" a face atom
6 face atoms at 1/2 ownership = 3 atoms
Section 8.3
Unit Cell Ownership of Atoms
A cube has 12 edges
It takes 4 cubes to "contain" an edge atom
12 edge atoms at 1/4 ownership = 3 atoms
Section 8.3
Unit Cell Ownership of Atoms
A cube has 8 corners
It takes 8 cubes to "contain" a corner atom
8 corner atoms at 1/8 ownership = 1 atom
Section 8.3
Coordination Number Coordination Number (CN)- the number of atoms that surround an atom in a crystal lattice. Simple Cubic (sc) Body Centered Cubic (bcc) Face Centered Cubic (fcc)
CN = 6
CN = 8
CN = 12
CN packing efficiency
Section 8.4
Types of Solids metallic M lo-hi MP ionic M-NM or PA hi MP network covalent near metalloid hi MP molecular NM-NM lo MP
Molecular Forces (dispersion, dipole, H-bonding) are still weak compared to ionic and network covalent forces
Summary
Bonding in C6H8
H H C H H C H C C C C H H H
Section 6.8
5 nodes 4 nodes 3 nodes
6 5 4
E
2 nodes 1 node MO theory
Section 6.5
3 2 1
0 nodes
Metallic Solids Band Theory Solids:
E
E
E
E
E
1 AO
Section 8.6
2 AO
4 AO
8 AO 16 AO
Avogadro's # AO
Metallic Solids: Band Theory conduction band E Fermi level Valence band
Metal
E=0
Fermi level
E
Band gap
E
Metallic conductor
Section 8.6
semiconductor
insulator
Interparticle Forces and Metallic Solids Metallic substances: what holds them together? Coulombic force of attraction between oppositely charged entities. cations & sea of VE
Interparticular force: Metallic bonds
Melting point: lo - hi
Section 8.6
Interparticle Forces and Ionic Solids Ionic substances: what holds them together? Coulombic force of attraction between cations & anions oppositely charged entities. Interparticle force
Ionic bond Melting point: High
Section 8.7
NaCl
CsCl
1 Unit Cell
8 Unit Cells
Coulomb's Law of Force kq1q2 F= r2 How can the force become stronger?
(Either more attractive or more repulsive) Larger numerator: Larger charge Smaller denominator: Closer distance Less shielding (vacuum shields less than water) The bottom line: atoms stick tightly when they have charge large and are close together
Section 1.7
Network Covalent Solids SiO2 ER = 3*8 = 24 e-s VE = 4 + 6 + 6 = 16 e-s 8 e-s / 2 = 4 bonds 8 e-s / 2 = 4 lone pairs Si O O
4 bonds 16 e-s 4 lone pairs
SiO2 O
Section 8.8
CO2 O Huh? O C Gas O
Si Sand
Network Covalent Solids SiO2 Sand, Quartz C Diamond, Graphite, Fullerenes, Nanotube ZnS Zinc Blende Si, Ge, GaP, BAs, InP - Semiconductors
How can you tell? They are near the metalloids (B,Si,Ge,As,Sb,Te,At). Mostly, you just have to memorize.
Section 8.8
Interparticle Forces and Network Covalent Solids
Network Covalent: what holds them together? Coulombic force of attraction between nuclei & shared e-s oppositely charged entities. Interparticle force
Covalent bond Melting point: High
Section 8.8
The Many Network Covalent Solids Of Carbon
graphite: A lubricant
Graphite
Section 8.8
The Many Network Covalent Solids Of Carbon
Buckyball or C60: No commercial uses (so far)
Section 8.8
The Many Network Covalent Solids Of Carbon
Nanotube: Way Cool. Can act as a conduct or semiconductor. Used to build small wires, diodes and transistors. Building part for tiny machines: nanotech
Section 8.8
The Many Network Covalent Solids Of Carbon
Diamond: An expensive gift & the hardest substance known
3-D Models: http://jas.eng.buffalo.edu/education/solid/unitCell/home.html
Section 8.8
Zinc Blende or ZnS
Good semiconductor, along with GaAs and InP, which have the same structure
Section 8.6
-cristobalite
High temperature SiO2
Si
O
Section 8.8
Aluminosilicates or Zeolites Composed of AlO4 and SiO4 units
Uses: 1) to exchange Ca2+ and Mg2+ for Na1+, producing "soft" water (ion exchange) 2) catalyst (lots of O - sites) 3) molecular sieves (a way to trap small molecules like water or gas)
Section 8.8
Clays Composed of AlO6 and SiO4 units
Uses: can be shaped and fired to form porcelin
Section 8.8
Interparticle Forces and Molecular Solids + dipole temporary permanent
dispersion forces dipole-dipole forces
All molecules Non-polar or polar Polar molecules
Hydrogen bonding
N-H, O-H, F-H
Section 7.2
Molecular Solids
H H H H H H H H
H
O
Ice
H
Naphthalene
I
H2 C C H2 H2 C C H2 H2 C
Stearic Acid
I
C H2 H2 C
Iodine
H3C
H2 C
C H2
H2 C
C H2
C H2
H2 C
C H2
H2 C
OH C H2 O
Which substance has the higher MP? a ionic KCl or C6H12O6 (glucose) molecular b network C (diamond) or CO2 molecular c ionic AlN or CaS ionic Chlorine--gas at 1 atm/25oC dmolecular Cl2 or I2 molecular Iodine--solid at 1 atm/25oC
Determine the type of compounds Ionic ~ network > molecular If both are ionic, larger charges > smaller charges If both are molecular, H-bonding > dipolar > DISPERSION > dispersion
Summary
Which one has the higher melting point: (A) (NH4)2S or (B) MgS? Which one has a higher boiling point: (A) SiO2 or (B) SO2 ? Which one has a higher melting point: (A) NH4Cl or (B) NCl3 ? Which one has a higher melting point: (A) CH3CH2CH2NH2 or (B) N(CH3)3 ?
Solid types summary
Type Metallic Particles atoms
(metals)
Forces
MP range
Examples Na, Cu, Ag, Fe NaCl, NH4Cl, MgO C, ZnS, SiO2, Si, Ge
metallic bonds variable
Ionic
ions
(M-NM)
ionic bonds
6002000 oC 6002000 oC
Network covalent
atoms
(non-metals and metalloids)
covalent bonds
Molecular
molecules
(covalent compounds)
intermolecular -260 (disp, D-D, H290 oC
bond)
H2O, sugar, naphthalene, stearic acid
Liquid crystals displays
-Each pixel of an LCD consists of a layer of perpendicular molecules aligned between two electrodes, and two polarizing filters. -By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass through in varying amounts, correspondingly illuminating the pixel.
Cd2+ I1(in center of cell)
What is the ionic formula for this compound? A) CdI2 B) Cd8I
B) Cd4I2 D) Cd8I2