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

23 CHEM 112 Bonding in Materials

Example Problems

3.! For each of the following pairs of

substances,

predict which will have the higher

melting point.

KBr Br2

SiO2 CO2

Ar Xe