Chem 106 Thursday Feb. 3, 2011

Transcription

1 Chem 106 Thursday Feb. 3, 2011 Chapter 13: -The Chemistry of Solids -Phase Diagrams - (no Born-Haber cycle) 2/3/2011 1

2 Approx surface area (Å 2 ) 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

3 Approx surface area (Å 2 ) BP 10 C 28 C Which C 5 H 12 alkane do you think has the highest boiling point? 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

4 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

5 Network Solids Diamond Graphite

6 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

7 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

8 Solid structures are determined by x-ray diffraction. crystal Area detector Rotating stage

9 X-rays bounce off different planes of atoms 500,00 small molecule structures now in Cambridge Crystallographic Data Center 55,500 protein and DNA structures now in Protein Data Bank

10 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/

11 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/

12 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/

13 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/

14 This is another repeating unit. But this is not the smallest repeating unit so it is not considered a proper unit cell. 2/3/

15 Crystal Lattice Unit Cells The 7 basic crystal systems CUBIC All sides equal length All angles are 90 degrees CHEM 106 2/3/

16 Cubic Unit Cells of Metals Simple cubic (SC) Body-centered cubic (BCC) Face-centered cubic (FCC) 2/3/

17 Units Cells of Metals (At least the pattern is not random ) Figure /3/

18 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. 2/3/

19 Units Cells of Metals Po has most Figure unusual valence electron structure (and packing pattern ) of all metals. 2/3/

20 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/

21 Number of Atoms per Unit Cell Unit Cell Type SC BCC FCC Net Number Atoms /3/

22 144 c 408 pm 408 pm Au radius = c 4 c c c 2 a 2 a 2 b b 2 * 408 r Au Use Pythagorean Theorem (it s a right triangle since it s a cubic lattice.) 576 pm 2/3/

23 Atom Packing in Unit Cells 2/3/

24 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/

25 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/

26 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/

27 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/

28 In zinc sulfide, the Zn 2+ cations occupy holes between S 2- anions. 2/3/

29 The sulfide ions occupy what type of unit cell? Simple cubic Simple cubic Body-centered... Face-centered Body-centered cubic 3. Face-centered cubic 2/3/

30 The sulfide ions occupy what type of unit cell? 1. Simple cubic 2. Body-centered cubic 3. Face-centered cubic 2/3/

31 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/

32 2/3/ g/cm d cm x10 g CuI 1.265x10 d pm 10 1cm x 605.1pm molcu 63.54gCu x atomcu 6.023x10 1molCu unitcell 4atomCu moli 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 m cm 10 pm 10 1m x pm or

33 Heating curves and Phase diagrams

34 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

35 Typical OWL heating/cooling curve problem

36 All substances have 2-step heating/cooling curves like this with different Temps and line lengths C 961 C 21 C Q total Q liquid Q freezing Q solid

37 961 C 1214 C 21 C J Q C 961 C 1214 C g J g Q ΔT mc Q liquid o o o liquid liqu liquid J Q C 21 C 961 C g J g Q ΔT mc Q solid solid o o o solid solid J Q g Q ΔH m Q mp mp fusion mp g J kj kj J J J J Q Q total total solid mp liquid total Q Q Q Q

38 Typical Phase Diagram B supercritical fluid

39 X X

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41 The best way to answer these is to draw your own phase diagram

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