Chem 106 Thursday Feb. 3, 2011 Chapter 13: -The Chemistry of Solids -Phase Diagrams - (no Born-Haber cycle) 2/3/2011 1
Approx surface area (Å 2 ) 253 258 Which C 5 H 12 alkane do you think has the highest boiling point? 1. Top 2. Middle 3. Bottom 223% 228% 288% 268 Top Middle Bottom 2/3/2011 2
Approx surface area (Å 2 ) 253 258 BP 10 C 28 C Which C 5 H 12 alkane do you think has the highest boiling point? 268 36 C This one has greater contact surface for intermolecular interactions. The more compact structure of neopentane presents a smaller surface for creation of London forces of attraction. 2/3/2011 3
Solid Types TYPE EXAMPLE FORCE Metallic Na, Fe Metallic Ionic NaCl Ion-Ion Molecular Ice, I 2 Dipole/Induced Dipole Network Diamond, Graphite Covalent Amorphous Glass Covalent 2/3/2011 4
Network Solids Diamond Graphite
Graphene.hin This is MO #105, one of the 100 -molecular orbitals calculated with the PM3 semi-empirical method. Graphene and graphite sheets have extensive regions of - electron clouds above and below the plane of the atoms. Graphene is a large single sheet of graphite. This is a small chunk of graphene (C 100 H 26 ) with H s around the edge. 2/3/2011 6
3.35 Å separation of layers in graphite. (This is clean graphite without adhering air molecules.) The lubricating properties of graphite are due to a ball bearing effect of small air molecules trapped between the layers. Molecular modeling shows that locally, the 3.35 Å separation must increase to accommodate the trapped molecules. 2/3/2011 7
Solid structures are determined by x-ray diffraction. crystal Area detector Rotating stage
X-rays bounce off different planes of atoms 500,00 small molecule structures now in Cambridge Crystallographic Data Center www.ccdc.cam.ac.uk 55,500 protein and DNA structures now in Protein Data Bank www.rcsb.org
Properties of Solids 1. Molecules, atoms or ions locked into a crystal lattice 2. Some of the particles are touching 3. Strong Intermolecular forces 4. Highly ordered, rigid, incompressible ZnS, zinc sulfide 2/3/2011 10
Crystal Lattice Regular 3-D arrangement of equivalent LATTICE POINTS in space. Lattice points define the UNIT CELL, which is smallest repeating internal unit that has the symmetry characteristic of the solid. 2/3/2011 11
Different unit cells could describe the same 2D (or 3D) lattice. You can generate the whole 2D (or 3D) structure by building up Unit Cells. 2/3/2011 12
If you build out the unit cell in all directions, you get the macroscopic crystal. NaCl is cubic. (This crystal has been cleaved ) 2/3/2011 13
This is another repeating unit. But this is not the smallest repeating unit so it is not considered a proper unit cell. 2/3/2011 14
Crystal Lattice Unit Cells The 7 basic crystal systems CUBIC All sides equal length All angles are 90 degrees CHEM 106 2/3/2011 15
Cubic Unit Cells of Metals Simple cubic (SC) Body-centered cubic (BCC) Face-centered cubic (FCC) 2/3/2011 16
Units Cells of Metals (At least the pattern is not random ) Figure 13.5 2/3/2011 17
Metals crystallize in bcc, fcc and others due to the differing orbital populations in metal atoms. In metals, the valence electrons are shared with neighbors. The different packing patterns are related to different number and types (s p or d) of valence electrons, and different nuclear charges. MO theory shows electrons in bands which are large delocalized MOs. http://www.chemguide.co.uk/atoms/bonding/metallic.html#top 2/3/2011 18
Units Cells of Metals Po has most Figure unusual 12.28 valence electron structure (and packing pattern ) of all metals. 2/3/2011 19
Cubic Unit Cells of Metals sc bcc fcc Like cutting an orange in 3 planes: you get halves->quarters- >octants 8 x 1/8 per corner = 1 8 x 1/8 per corner = 1 1 x 1 in center = 1 8 x 1/8 per corner = 1 6 x 1/2 in faces = 3 2/3/2011 20
Number of Atoms per Unit Cell Unit Cell Type SC BCC FCC Net Number Atoms 1 2 4 2/3/2011 21
144 c 408 pm 408 pm Au radius = c 4 c c c 2 a 2 a 2 b b 2 * 408 r Au 576 4 144 2 2 2 Use Pythagorean Theorem (it s a right triangle since it s a cubic lattice.) 576 pm 2/3/2011 22
Atom Packing in Unit Cells 2/3/2011 23
Atom Packing in Unit Cells Assume atoms are hard spheres and that crystals are built by PACKING of these spheres as efficiently as possible. 2/3/2011 24
Copper: cubic close-pack Atoms in the 3rd ( C ) layer fit into pockets in the 2 nd layer. However these do not lineup with atoms in the 1 st layer. Cubic closepack creates face-centered unit cells. Here is one Atoms in the 2 nd ( B ) layer fit right into pockets in the 1 st layer. A B C A 2/3/2011 25
Zinc: hexagonal close-pack Hexagonal closepack creates hexagonal unit cells. Here is one Atoms in the 2 nd ( B ) layer fit right into pockets in the 1 st layer. Atoms in the 2 nd layer do lineup with atoms in the 1 st layer. 2/3/2011 26
Ionic Unit Cells (CsCl) Lattice points are Cl - ions (on corners), and Cs + in hole OR Lattice points as Cs + ions, and Cl - ion in hole (Either way, you get 1 Cs + and 1 Cl - per unit cell.) 2/3/2011 27
In zinc sulfide, the Zn 2+ cations occupy holes between S 2- anions. 2/3/2011 28
The sulfide ions occupy what type of unit cell? 108 23 41 1. Simple cubic Simple cubic Body-centered... Face-centered... 2. Body-centered cubic 3. Face-centered cubic 2/3/2011 29
The sulfide ions occupy what type of unit cell? 1. Simple cubic 2. Body-centered cubic 3. Face-centered cubic 2/3/2011 30
BOARD This is an unusual unit cell, so OWL shows you a picture. Per unit cell: 4 Cu + ions (inside) 8 x 1/8 I - ions at corners 6 x ½ I - ions on faces 4 I - ions CuI 2/3/2011 31
2/3/2011 32 3 3 22 21 3 10 3 23 23 5.712 g/cm d cm 2.2155x10 g CuI 1.265x10 d pm 10 1cm x 605.1pm molcu 63.54gCu x atomcu 6.023x10 1molCu unitcell 4atomCu moli 126.9 g I x atomi 6.023x10 I 1 mol cell unit atomi 4 v m d cell unit volume of I mass of Cu mass of cell unit volume of cell unit per CuI mass of v m d density 3 2 3 12 3 m cm 10 pm 10 1m x pm 605.1 or
Heating curves and Phase diagrams
All substances have 2-step heating/cooling curves like this with different Temps and line lengths. Q gas = mc gas T Q boil = mh vaporization -> Q liquid = mc liquid T Q melt = mh fusion -> Q solid = mc solid T
Typical OWL heating/cooling curve problem
All substances have 2-step heating/cooling curves like this with different Temps and line lengths. 1214 C 961 C 21 C Q total Q liquid Q freezing Q solid
961 C 1214 C 21 C 2429.9J Q C 961 C 1214 C g 0.2850 J 33.70 g Q ΔT mc Q liquid o o o liquid liqu liquid 7539.4 J Q C 21 C 961 C g 0.2380 J 33.70 g Q ΔT mc Q solid solid o o o solid solid 3740.0 J Q 110.8 33.70 g Q ΔH m Q mp mp fusion mp g J kj kj J J J J 13.7 13.703 13703 Q 7539.4 3734.0 2429.9 Q total total solid mp liquid total Q Q Q Q
Typical Phase Diagram B supercritical fluid
X X
54. 1.00 The best way to answer these is to draw your own phase diagram. 0.72 116 116 120 209