crystalline structures edward a. mottel department of chemistry rose-hulman institute of technology
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Crystalline StructuresEdward A. Mottel
Department of Chemistry
Rose-Hulman Institute of Technology
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Crystalline Solid State
Study of the arrangement of atoms/ions in metallic and ionic crystals.
Enables the calculation of the size of atoms/ions.
Allows the "environment" (the number of atoms/ions and the types of atoms/ions) surrounding each atom/ion to be studied.
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Physical PropertiesRelated to Solid Structure
Density Luster Hardness Electrical Properties Melting Point Magnetic Properties
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Distinctions Between Solid Structures
Crystalline versus Amorphous Solids Crystal Structure versus Crystal Morphology Equivalent Sphere versus Ionic Structures
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Unit Cells
Simple Cubica = b = c
= 90°
ab
c
Triclinica b c
90°
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Crystal Structure Definitions
Unit cell• cell dimensions• unit cell length (a, b, c)• cell angles ()
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Crystal Structure Definitions
Cell relationships• edge• face-diagonal• body-diagonal• cell volume
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Crystal Structure Definitions
Cell relationships• edge• face-diagonal• body-diagonal• cell volume
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Crystal Structure Definitions
Cell relationships• edge• face-diagonal• body-diagonal• cell volume
If the cell edge is a, how long is the face diagonal?
If the cell edge is a, how long is the body diagonal?
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Crystal Structure Definitions
Cell relationships• edge• face-diagonal• body-diagonal• cell volume
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The Unit CellCrystal Structure Definitions
Begin working on page J-4 of laboratory manual
Refer to page J-1 for definitions• Unit Cell
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Solid State Model Kit
Obtain one kit for every 3-4 people. Sit in a circle so that everyone can see the models
as they are being built. Refer to pg. 5 of the Model Kit Manual (in the box)
for instructions• how to select the plastic base to use.• which holes of the base to use.• how to build the models.• how to take them apart.
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Equivalent Sphere StructuresCrystal Structure Definitions
Start at page J-5 of laboratory manual; work through page J-10
Refer to page J-1 for definitions• Net atoms per unit cell• Percentage void space (packing efficiency)• Coordination Number (CN)
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Questions to ConsiderWhen Studying Solid State Structures
How do the atoms touch? What is the length of the edge of the unit cell in
terms of the atomic radii? How many net atoms are there per unit cell? What is the percentage void space in the structure? Build the primitive (simple) unit cell (pg. 9, 102)
• Build the small cube, then the large cube• Answer questions on page J-5 of lab manual
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Solid State Model KitModels to Build
Primitive (simple) unit cell (pg. 9, 102)• Build the small cube, then the large cube• Page J-5 of lab manual
Body-Centered Cubic (bcc) pg 18, J-6 Face-Centered Cubic (fcc) pg 27, J-7 Cubic Closest Pack (ccp) pg 26, J-8
• Shaded area and hollow numbers Hexagonal Closest Pack (hcp) pg 24, 99, J-8
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Simple (Primitive) Cubic
1) 6 2) 2r 3) 22 r 4) 23 r 5) 1 net atom per unit cell 6) 47.6%
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Body-Centered Cubic
1) 8 2) 8 3) 4r 4) 4r/3 5) 2 net atoms per unit cell 6) 31.9%
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Face-Centered Cubic
1) 12 2) 4r 3) 22 r 4) 4 net atoms per unit cell 5) 25.9%
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Equivalent Sphere Summary
Structure
Along which dimensionsof a cube do the atoms
touch Length
simple (primitive)cubic
body-centeredcubic
face-centeredcubic
edge 2 r
body-diagonal
face-diagonal
4 r
4 r
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Diamond Hardest naturally occurring material Strong because
• strong covalent bonds• 3-dimensional strength
Same structure is formed by• silicon and germanium
Similar structure formed by several semiconducting materials• GaAs, GaP
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Diamond StructureAtoms occur at
the corners of theunit cell
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Diamond Structure
Atoms occur atthe face centersof the unit cell
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Diamond StructureAtoms occur atfour positions
withinthe unit cell
The four positionsare at the centers
of alternatesmaller cubes
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Diamond StructureAtoms occur atfour positions
withinthe unit cell
The four positionsare at the centers
of alternatesmaller cubes
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Diamond StructureAtoms occur atfour positions
withinthe unit cell
The four positionsare at the centers
of alternatesmaller cubes
Atoms occur atthe corners of the
unit cell
Atoms occur atthe face centersof the unit cell
How many net carbon atoms are there per unit cell?
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Diamond Structure
Some atomstouch along
thebody-diagonal
How long is thebody-diagonalin terms of r?
The density of diamond is 3.51 g·cm3.What is the radius of a carbon atom?
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Graphite Structure
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How many spheres can fit into the following square (2-D)
17
7
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How many spheres can fit into the following square (2-D)
49
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How many spheres can fit into the following square (2-D)
52 + 8/2
Hexagonal packing is efficient.
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Experiment JJ: Solid State IIElectrical Resistance
Ele
ctr
ical
re
sis
tan
ce
Temperature
A
B
C
Based on your observations, which type of material corresponds to which line?
metal
semiconductor
superconductor
metal
semiconductor
superconductor
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Sodium nitrate crystal formation Bobby Pin heat treatment Copper wire work hardening
Experiment JJ: Solid State IIStructure
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Solid State Model KitModels to Build
Cubic Closest Pack (ccp) pg 26, J-8• Shaded area and hollow numbers
Hexagonal Closest Pack (hcp) pg 24, 99, J-8 Hole Calculation, Radius Ratio and
Coordination Number pg 93, J-11• How is r/R calculated?
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Cesium ChlorideTwo Different Kinds of Ions
One type of ionoccurs at thecorners ofa cube The other ion
occurs at thecenter ofthe cell
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One type of ionoccurs at
the cornersof a cube
Sodium ChlorideA Different Structure with Two Kinds of Ions
the centersof a each face
The other ionoccurs at
the center ofthe each edge
the center ofthe cell
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Questions to ConsiderWhen Studying Solid State Structures
How do the ions touch? What is the length of the edge of the unit cell
in terms of the ionic radii? How many net ions are there per unit cell? What is the percentage void space in the
structure?
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Ionic Structures
Cesium Chloride (CsCl) pg 96• Answer questions on page J-12 of lab
manual Rock Salt (NaCl) pg 33, 31
• Answer questions on page J-13 of lab manual
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Cesium Chloride Structure
i) 8, 8, 0 ii) 8, 8, 0 iii) cubic hole iv) 2r+ + 2r-
v) 1 cation vi) 1 anion
vii) 5.50/3 = 3.18 Å viii) 32.0 Å3
ix) 30.3%
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Rock Salt Structure
i) 6, 6, 0 ii) 6, 6, 0 iii) octahedral hole iv) 2r+ + 2r-
v) 4 cations vi) 4 anions
vii) 125 Å3
viii) 38.0%
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