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1 CHEM 112 Bonding in Materials
Bonding in Solid Materials
What types of bonds would you expect for…
Salts:
Covalent Molecules:
Elements:
Noble gases
Nonmetals:
S, P, Se
C
Diatomic gases
Metals
Metalloids (semi-metals)
2 CHEM 112 Bonding in Materials
Importance of INTERmolecular Forces
3 CHEM 112 Bonding in Materials
FYI: Phase Diagrams
Plot of pressure vs. temperature of the system
showing the boundaries between the
phases.
•! coexistence curves
•! triple point
•! normal melting point
•! normal boiling point
•! pressure dependence of boiling point
•! pressure dependence of melting point
•! critical point
•! supercritical fluid
•! Predict what happens when the pressure
and/or temperature of the system is
changed
4 CHEM 112 Bonding in Materials
Structure of Solids
•! Amorphous: no regular organization at a molecular level, eg. glass, coal
•! Crystalline: regular 3-D array of atoms or molecules, eg. NaCl, ice, sugar
5 CHEM 112 Bonding in Materials
Structure of Crystalline Solids:
Unit Cells
Crystal lattice: 3-D array of
atoms
Unit cell: repeating unit of
crystal lattice
6 CHEM 112 Bonding in Materials
Bonding in Ionic Solids
Examples of Ionic Solids:
•!NaBr
•!CaCO3
•!NH4Cl
•!FeCl2
7 CHEM 112 Bonding in Materials
Note that multiple types of bonding can be
present in the same compound
Bonding in ionic solids
Barium
Oxygen
Titanium
8 CHEM 112 Bonding in Materials
Bonding in Molecular Solids
Examples of Molecular/Atomic solids:
•! Ar (atomic solid)
•! water (ice)
•! CO2 (dry ice)
•! hydrocarbons (gasoline)
•! alcohols
•! sugar
•! methane
9 CHEM 112 Bonding in Materials
Bonding in Network
Covalent Solids
Examples of Network Covalent Solids:
•!SiC
•!BN
•!Metalloids
•!B
•!SiO2 (quartz)
•!C (diamond)
•!C (graphite) 2-D silicate sheet, Si2O5
2-
10 CHEM 112 Bonding in Materials
Allotropes of Carbon •!Structure Uses •!1. Diamond
•!4 ! bonds to each C hardest substance known (Gem)
•!sp3 hybridization abrasive, drill bits, cutting tools
•!tetrahedral, dense
•!
•!
•!2. Graphite (crystalline)
•!3 ! bonds to each C conducts current, soft: lubricant
•!planar sp2 hybridization batteries (as electrode), pencils •!delocalized "-bonds van der waals forces between planes
•!
•!Carbon Black (amorphous) tires, ink pigments, carbon paper
•!Charcoal (amorphous) adsorb molecules in filters
•!Coke (amorphous) reducing agent in metallurgical operation
•!3. Fullerenes
•!3 ! bonds to each C No uses:
•!sp2 hybridization found in soot
•!delocalized "-bonds
•!MOLECULAR form C60
•!
•!4. Nanotubes •!Sheets of graphite rolled up, nanoscale electronic circuits
•!capped by half of C60 molecule stronger than steel on nanoscale
•!Multiwall or single walled strong fibers with polymers
•!Armchair (metallic behavior)
•!Zigzag (diameter dictates semi-
•!conductor or metallic behavior)
11 CHEM 112 Bonding in Materials
Ceramics
Inorganic, nonmetallic solids
•! Typically hard and brittle
–! Less dense than metals, lighter
–! More elastic than metals
–! Resist corrosion and wear, don’t deform
•! Stable at high temperatures
–! High melting
•! Can be covalent network and/or ionic
–! Usually electrical insulators
Crystalline:
–! Oxides (Al2O3, ZrO2,BeO)
–! Carbides (SiC, Ca2C)
–! Nitrides (BN)
–! Silicates (SiO2 mixed with metal oxides)
–! Aluminosilicates (Al2O3 + SiO2 + metal oxides:
Mica, Talc, Pottery, Clay)
Amorphous (glasses)
12 CHEM 112 Bonding in Materials
Silicates; Si always found in nature in combination
with O
1) Tetrahedral orthosilicate ion
(SiO44- units); found in very
few silicate minerals
Example: Zircon ZrSiO4
One vertice linked: Disilicate
ion Si2O76-
Example: hardystonite Ca2Zn
(Si2O7)
Positive ions
balance the charge;
hold chains or
sheets together
Four types of structures;
13 CHEM 112 Bonding in Materials
Most Silicate Minerals are linked
tetrahedra
3) Infinite 2-D Sheet , 2 vertices linked: (Si2O5)x2-
Example: talc Mg3(Si2O5)2(OH)2
4) 3-D infinite Network, all four vertices linked: SiO2
Examples: quartz, sand, glass
2) Infinite Single Strand Chain, 2 vertices linked:
(SiO3)x2- or Si2O6
4-
Examples: asbestos (fibrous silicate minerals),
enstatite MgSiO3
14 CHEM 112 Bonding in Materials
Fused Silica Glass
GLASS is made from SiO2
Excellent materials properties:
Transparent in visible and ultraviolet
High index of refraction
Low thermal conductivity
Low thermal expansion coefficient
But… Tg = 1600°C for fused silica (too high)
Additives lower processing temperature Usually oxides like Na2O, CaO, B2O3, etc.
Break up covalent ring network with ionic bonds
Lower Tg (and therefore processing temp.)
Example: soda-lime glass (window glass),
contains Na2O, CaO Softens at 600°C
15 CHEM 112 Bonding in Materials
Changing the
Properties of Glass
Soda-lime glass: SiO2, Na2O, CaO
Soda lime glass + CoO
deep blue (cobalt glass)
Use K2O instead of Na2O
harder glass, higher mp
Using PbO instead of CaO
denser “leaded” glass
greater refractive index
(bends light differently)
Pyrex Glass “borosilicate”
Contains B2O3 in addition to SiO2, Na2O
Has low thermal expansion coefficient
(doesn’t crack when rapidly heated or
cooled)
Glass with AgCl or AgBr added
photochromic (dark when exposed to light,
clear with little or no light)
16 CHEM 112 Bonding in Materials
Bonding in Metallic Solids
Examples of Metallic Solids:
•!Mg
•!Na
•!W
Free Electron Model
Metals are positive ions in a “sea” of nearly free
electrons.
Electrons bind metal ions together but are free to
roam the crystal lattice.
Explains malleability, ductility and high electrical and thermal conductivity.
17 CHEM 112 Bonding in Materials
Classes of Solids
Kind of Interaction Example
Ionic
Atomic
Molecular
Covalent Network
Metals
18 CHEM 112 Bonding in Materials
Bonding in the elements
What types of bonds would you expect for…
Metals
Metalloids (semi-metals)
Nonmetals – noble gases
Nonmetals – diatomic gases
Nonmetals – S, P, Se
Nonmetals – C
19 CHEM 112 Bonding in Materials
Summary of Bonding in Solids
Crystal Type
Unit Forces Example Properties
atomic atoms dispersion Ar, Kr v. low M.P.
soft
molecular
polar or
nonpolar
molecules
dispersion
dipole-dipole
H-bonding
sugar
CH4, CO2
H2O
soft, low M.P.
covalent
(network)
atoms in
covalent
network
covalent
bonds
diamond
graphite
quartz high M.P., hard
ionic
cations and
anions electrostatic NaCl high M.P.,
brittle
metallic atoms metallic
bonds
metals
Cu, Fe,
Al, Ni
wide range of
M.P., softer,
malleable, ductile
20 CHEM 112 Bonding in Materials
Bonding in Solids
MAIN GROUPS MAIN GROUPS
1A
1
7A
1 7
8A
18
1
H 1.00 8
2A 2
3A 1 3
4A 1 4
5A 1 5
6A 1 6
1
H 1.00 8
2
He 4.00 3
3 Li
6.94 1
4 Be 9.01 2
5 B
10.811
6 C
12.011
7 N
14.007
8 O
15.999
9 F
18.998
10 Ne
20.180
11
Na 22.990
12
Mg 24.305
13
Al 26.982
14
Si 28.086
15
P 30.974
16
S 32.066
17
Cl 35.453
18
Ar 39.948
19 K
39.098
20 Ca
40.078
31 Ga
69.723
32 Ge 72.6 1
33 As
74.992
34 Se
78.9 6
35 Br
79.904
36 Kr
83.8 0
37
Rb 85.468
38
Sr 87.6 2
49
In 114.82
50
Sn 118.71
51
Sb 121.76
52
Te 127.60
53
I 126.90
54
Xe 131.29
55 Cs
132.91
56 Ba
137.33
81 Tl
204.38
82 Pb 207 . 2
83 Bi
208.98
84 Po [209 ]
85 At
[210 ]
86 Rn [222 ]
87 Fr
[223 ]
88 Ra [226 ]
114
[285 ]
116
[289 ]
118
[293 ]
Atomic
Molecular
Network covalent
Metallic
21 CHEM 112 Bonding in Materials
Example Problems
1.! Which type of crystal will form when
C6H6 (benzene) solidifies? 1. ionic
2. molecular
3. metallic
4. covalent-network
5. amorphous
22 CHEM 112 Bonding in Materials
Example Problems
2.! Indicate the type of crystal
(molecular, metallic, covalent-
network, or ionic) each of the following
would form upon solidification:
1.! Zr
2.! N2O4
3.! SiO2
4.! Ne
5.! Ni(ClO3)2
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