SOlids - John Kotz

7/30/2019 SOlids - John Kotz

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Metallic and Ionic SolidsSect ion 13.4Metallic and Ionic SolidsMetallic and Ionic SolidsSect ion 13.4Sect ion 13.4 Types of SolidsTable 13.6Types of SolidsTypes of SolidsTab le 13 .6Tab le 13 .6TYPE EXAMPLE FORCE

Ionic NaCl, CaF2, ZnS Ion-ion

Metallic Na, Fe Metallic

Molecular Ice, I2 Dipole

Ind. dipole

Network Diamond Extended

Graphite covalent

TYPETYPE EXAMPLEEXAMPLE FORCEFORCE

IonicIonic NaClNaCl, CaF, CaF22,, ZnSZnS Ion-ionIon-ion

MetallicMetallic NaNa, Fe, Fe MetallicMetallic

MolecularMolecular Ice, IIce, I22 DipoleDipole

IndInd . dipole. dipole

NetworkNetwork DiamondDiamond ExtendedExtended

GraphiteGraphite covalentcovalent

Network SolidsNetwork SolidsNetwork SolidsDiamondDiamond

GraphiteGraphite

Network SolidsNetwork Solids

A com pari son of di amon d (pu re carb on)A co mpar iso n of d iamo nd (p ure c arbo n)with silicon.with silicon.

Properties of SolidsProperties of SolidsProperties of Solids

1. Molecules, atoms or

ions locked into a

CRYSTAL LATTICE

2. Particles are CLOSE

together

3. STRONG IM for ces

4. Highly ordered, rigid,

incompressible

1. Molecules, atoms or1. Molecules, atoms or

ions locked into aions locked into a

CRYSTAL LATTICECRYSTAL LATTICE

2. Particles are CLOSE2. Particles are CLOSE

togethertogether

3. STRONG IM for ces3. STRONG IM for ces

4. Highly ordered, rigid,4. Highly ordered, rigid,

incompressibleincompressible

ZnSZnS, zinc sulfide, zinc sulfide

Crystal LatticesCrystal LatticesCrystal LatticesRegular 3-D arrangements of equivalent

LATTICE POINTS in s pace.

The lattice points define UNIT CELLS ,the smallest repeating internal unit that hasthe symmetry characteristic of the solid.

There are 7 basic crystal systems, but we are

only concerned with CUBIC.

Regular 3-D arrangements of equivalentRegular 3-D arrangements of equivalent

LATTICE POINTS in s pace.LATTICE POINTS in space.

The lattice points defineThe lattice points define

UNIT CELLSUNIT CELLS ,,

the smallest repeating internal unit that h asthe smallest repeating internal unit that has

the symmetry characteristic of the solid.the symmetry characteristic of the solid.

There are 7 basic crystal systems, but we areThere are 7 basic crystal systems, but we are

only concerned withonly concerned with CUBICCUBIC..


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Cubic Unit CellsCubic Unit CellsCubic Unit CellsAll anglesare 90 degrees

All sidesequal length

Cubic Unit Cells of MetalsFigure 13. 28Cubic Unit Cells of MetalsCubic Unit Cells of MetalsFigure 13. 28Figure 13. 28Simple

cubic (SC)

Simple

cubic (SC) Body-Body-

centeredcentered

cubic (BCC)cubic (BCC)Face-Face-

centeredcentered

cubic (FCC)cubic (FCC)

Simple cubic unit cell.

Note that each atom is at a corner of aunit cell and is shared among 8 unitcells.

Simple Cubic Unit CellFigure 13. 28Simple Cubic Unit CellSimple Cubic Unit CellFigure 13. 28Figure 13. 28

Body-Centered Cubic Unit CellBody-Centered Cubic Unit CellBody-Centered Cubic Unit CellFace Centered Cubic

Unit Cell

Face Centered CubicFace Centered CubicUnit CellUnit Cell

Ato m at each cub e cor ner p lus atom i n each

cube face.

Ato m at each cub e cor nerAto m at each cub e cor ner plusplus atom in eachatom in each

cube face.cube face.

Crystal LatticesPacking of Atoms or Ions

Crystal LatticesCrystal LatticesPacking of Atoms or IonsPacking of Atoms or Ions

Assu me atom s are

hard spheres and

that crystals are

built by PACKINGof these spheresas efficiently as

possible.

FCC is more

efficient than

either BC or SC.

Assu me atom s areAss ume ato ms are

hard spheres andhard spheres and

that crystals arethat crystals are

built bybuilt by PACKINGPACKINGof these spheresof these spheres

as efficiently asas efficiently as

possible.possible.

FCC is moreFCC is more

efficient thanefficient than

either BC or SC.either BC or SC.

See Closer Look,See Closer Look, pppp. 622-623. 622-623


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Packing of C60molecules. Theyare arranged atthe lattice pointsof a FCC lattice.

Crystal LatticesPacking of Atoms or Ions

Crystal LatticesCrystal LatticesPacking of Atoms or IonsPacking of Atoms or Ions Number of Atoms per Unit CellNumber of Atoms per Unit CellNumber of Atoms per Unit Cell

Unit Cell Type Net Number Atoms

SC 1

BCC 2

FCC 4

Unit Cell Type

Unit Cell Type Net Number AtomsNet Number Atoms

SCSC 11

BCCBCC 22

FCCFCC 44

Simple Ionic CompoundsSimple Ionic CompoundsSimple Ionic Compounds

Lattices of many simple ionic solids are builtLattices of many simple ionic solids are builtby taking a SC or FCC lattice of ions of oneby taking a SC or FCC lattice of ions of onetype and placing ions of opposite charge intype and placing ions of opposite charge inthe holes in the lattice.the holes in the l attice.

EXAMPLE:EXAMPLE: CsClCsCl has a SC lattice of Cshas a SC lattice of Cs ++ ionsionswithwith ClCl-- in the center.in the center.


CsClCsCl has a SC lattice ofhas a SC lattice ofCsCs++ ions withions with ClCl-- in thein thecenter.center.

1 unit cell has 11 unit cell has 1 ClCl-- ionion

plusplus(8 corners )(1/8 Cs(8 corners)(1/8 Cs ++ perper

corner)corner)

= 1 net Cs= 1 net Cs ++ ion.ion.


Salts with formulaSalts with formulaMX can have SCMX can have SC

structure butstructure butnot salts withnot salts withformula MXformula MX22 ororMM22XX

Construction of NaClConstruction ofConstruction of NaClNaClWe begin with a cube ofWe begin with a cube ofClCl-- ions. Add moreions. Add more ClCl-- ions inions in

the cube faces, and then addthe cube faces, and then add NaNa++ ion in the octahedralion in the octahedralholes.holes.


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The Sodium Chloride LatticeThe Sodium Chloride LatticeThe Sodium Chloride Lattice

NaNa++ ions are inions are inOCTAHEDRALOCTAHEDRAL holesholesin a face-centeredin a face-centeredcubic lattice ofcubic lattice ofClCl--

ions.ions.

Many common salts have FCC arrangementsMany common salts have FCC arrangements

of anions withof anions with cationscations inin OCTAHEDRALOCTAHEDRALHOLESHOLES e.g., salts such as CA = e.g., salts such as CA = NaClNaCl

FCC lattice of anions ----> 4 AFCC lattice of anions ----> 4 A --/unit cell/unit cell

CC++ in octahedral holes ---> 1 Cin octahedral holes ---> 1 C ++ at centerat center

+ [12 edges 1/4 C+ [12 edges 1/4 C ++ per edge]per edge]

= 4 C= 4 C++ per unit cellper unit cell

The Sodium Chloride LatticeThe Sodium Chloride LatticeThe Sodium Chloride Lattice

Comparing NaCl and CsClComparingComparing NaClNaCl andand CsClCsCl

Even though their formulas have onecation and one anion, the lattices ofCsCl and NaCl are different.

The different lattices arise from the factthat a Cs+ ion is much larger than a Na+

ion.

Common Ionic SolidsCommon Ionic SolidsCommon Ionic Solids

Titanium dioxide,Titanium dioxide,TiOTiO22

There are 2 netThere are 2 netTiTi4+4+ ions and 4ions and 4net Onet O2-2- ions perions perunit cell.unit cell.


Zinc sulfide,Zinc sulfide, ZnSZnS

The SThe S2-2- ions are inions are in

TETRAHEDRALTETRAHEDRALholes in the Znholes in the Zn2+2+

FCC lattice.FCC lattice.

This gives 4 netThis gives 4 netZnZn2+2+ ions and 4ions and 4net Snet S2-2- ions.ions.


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Fluorite or CaF2

FCC lattice of Ca2+

ions

This gives 4 netCa2+ ions.

F- ions in all 8tetrahedral holes.

This gives 8 net F-

ions.

SOlids - John Kotz

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