Importance of INTER molecular Forces FYI: Phase …courses.chem.psu.edu/chem112/Fall/Lecture Notes/LSV Lecture Notes...Importance of INTER molecular Forces CHEM 1 12 Bonding in Materials

1 CHEM 112 Bonding in Materials

Importance of INTERmolecular Forces


FYI: Phase Diagrams

Plot of pressure vs. temperature of the system showing the

boundaries between the phases.

•! normal melting point

•! pressure dependence of melting point

•! normal boiling point

•! pressure dependence of boiling point

•! critical point

•! triple point

•! supercritical fluid

•! coexistence curves

•! Predict what happens when the pressure and/or temperature

of the system is changed


Structure of Solids

•! Amorphous: no regular organization at a molecular level. Examples:___________________

•! Crystalline: regular 3-D array of atoms or molecules. Examples:_______________________


Structure of Crystalline Solids:

Unit Cells

Crystal lattice: 3-D array of atoms

Unit cell: repeating unit of crystal

lattice


Classes of Solids Atomic Solids

(noble gases)

Molecular Solids

(VDW forces; discrete molecules, includes polymers)

Covalent Network Solids

(lattice of covalent bonds)

Ionic Solids

(salts; ionic bonds)

Metals

(metallic bonds; also alloys)


Bonding in Molecular Solids

Examples of Molecular/Atomic solids:

•! Ar (atomic solid)

•! CO2 (dry ice)

•! hydrocarbons (gasoline)

•! alcohols

•! sugar

•! water (ice)

•! methane


Bonding in Network Covalent

Solids

Examples of Network Covalent Solids:

•!SiC

•!BN

•!Metalloids

•!B

•!SiO2 (quartz)

•!C (diamond)

•!C (graphite)

2-D silicate sheet, Si2O52-


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

COVALENT NETWORK

2. Graphite (crystalline)

3 ! bonds to each C conducts current, soft: lubricant

planar sp2 hybridization batteries (as electrode), pencils

delocalized "-bonds

COVALENT NETWORK 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: found in soot C60

sp2 hybridization

delocalized "-bonds

MOLECULAR form

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)


Bonding in Ionic Solids

Examples of Ionic Solids:

•!NaBr

•!CaCO3

•!NH4Cl

•!FeCl2


Note that multiple types of bonding can be

present in the same compound

Bonding in ionic solids

Barium

Oxygen

Titanium


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.


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)


Silicates;

Si is always found in nature in combination with O

1a) Tetrahedral orthosilicate ion (SiO44-

units); found in very few silicate minerals

Example: Zircon ZrSiO4

1b) One vertice linked: Disilicate ion Si2O76-

Example: hardystonite Ca2Zn(Si2O7)

Positive ions balance the

charge; hold chains or

sheets together

Four types of structures;


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


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 (high E cost)

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


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)

Add AgCl or AgBr particles, precipitate out Ag(s)

photochromic (dark when exposed to light, clear with little or no light)


Cement is a glass H2O

Ca3SiO5 #$ Ca3Si2O7·3H2O + Ca(OH)2

Ca2SiO4 glassy, ca. 70% of cement (crystalline)

crystalline silicate powders

Cement is a composite material:

glassy and crystalline phases in a heterogeneous mixture

Composite: two or more materials making up a ceramic

Result: tougher ceramic

Most effective method: add fibers to ceramic material.

Example: SiC fibers added to aluminosilicate glass.

Fiber must have a length %100 times its diameter.

Carbon nanotubes are added to polymer resins: create high strength materials

Ceramics Composites


Aluminosilicates Made of Al2O3 + SiO2 + Other metal oxides & Replace Si4+ in sheets with Al3+

& Ropes/sheets are more negative; held together more strongly than

silicates

Clay (ceramic) hardening

Cement

Zeolites Crystalline aluminosilcates

Well-defined structures

Porous (cage-like)

Naturally occurring and man-made

Molecular sieves

Variety of pore sizes and uses


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


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


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


Example Problems

1.! Which type of crystal will form when C6H6 (benzene)

solidifies? 1. ionic

2. molecular

3. metallic

4. covalent-network

5. amorphous


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


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

Documents

Importance of INTER molecular Forces FYI: Phase …courses.chem.psu.edu/chem112/Fall/Lecture Notes/LSV Lecture Notes...Importance of INTER molecular Forces CHEM 1 12 Bonding in Materials