SOlids - John Kotz
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Transcript of 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.
Simple Ionic CompoundsSimple Ionic CompoundsSimple Ionic Compounds
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.
Simple Ionic CompoundsSimple Ionic CompoundsSimple Ionic Compounds
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.
Common Ionic SolidsCommon Ionic SolidsCommon Ionic Solids
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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Common Ionic SolidsCommon Ionic SolidsCommon Ionic Solids
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.