Metallic and Ionic Solids Sections 13.6-8 To play the movies and simulations included, view the presentation in Slide Show Mode.

Types of Solids Table 13.6 TYPE EXAMPLE FORCE Ionic NaCl, CaF2, ZnS Ion-ion Metallic Na, Fe Metallic Molecular Ice, I2 Dipole Ind. dipole Network Diamond Extended Graphite covalent

Network Solids Diamond Graphite

Network Solids A comparison of diamond (pure carbon) with silicon.

Properties of Solids 1. Molecules, atoms or ions locked into a CRYSTAL LATTICE 2. Particles are CLOSE together 3. STRONG IM forces 4. Highly ordered, rigid, incompressible ZnS, zinc sulfide

Crystal Lattices Regular 3-D arrangements of equivalent LATTICE POINTS in space. Lattice points define UNIT CELLS smallest repeating internal unit that has the symmetry characteristic of the solid.

Cubic Unit Cells There are 7 basic crystal systems, but we are only concerned with CUBIC. All sides equal length All angles are 90 degrees

Cubic Unit Cells of Metals Figure 13.24 Simple cubic (SC) Body-centered cubic (BCC) Face-centered cubic (FCC)

Units Cells for Metals Figure 13.25

Simple Cubic Unit Cell Figure 13.28 Note that each atom is at a corner of a unit cell and is shared among 8 unit cells.

Body-Centered Cubic Unit Cell

Face Centered Cubic Unit Cell Atom at each cube corner plus atom in each cube face.

Atom Packing in Unit Cells Assume atoms are hard spheres and that crystals are built by PACKING of these spheres as efficiently as possible.

Atom Packing in Unit Cells

Crystal Lattices— Packing of Atoms or Ions FCC is more efficient than either BC or SC. Leads to layers of atoms. See Closer Look, pp. 541

Packing of Atoms or Ions Crystal Lattices— Packing of Atoms or Ions Packing of C60 molecules. They are arranged at the lattice points of a FCC lattice.

Number of Atoms per Unit Cell Unit Cell Type Net Number Atoms SC BCC FCC 1 2 4

Atom Sharing at Cube Faces and Corners Atom shared in corner --> 1/8 inside each unit cell Atom shared in face --> 1/2 inside each unit cell

Simple Ionic Compounds Lattices of many simple ionic solids are built by taking a SC or FCC lattice of ions of one type and placing ions of opposite charge in the holes in the lattice. EXAMPLE: CsCl has a SC lattice of Cs+ ions with Cl- in the center.

Simple Ionic Compounds CsCl has a SC lattice of Cs+ ions with Cl- in the center. 1 unit cell has 1 Cl- ion plus (8 corners)(1/8 Cs+ per corner) = 1 net Cs+ ion.

Simple Ionic Compounds Salts with formula MX can have SC structure — but not salts with formula MX2 or M2X

Two Views of CsCl Unit Cell Either arrangement leads to formula of 1 Cs+ and 1 Cl- per unit cell

NaCl Construction Na+ in octahedral holes FCC lattice of Cl- with Na+ in holes

Octahedral Holes in FCC Lattice

The Sodium Chloride Lattice Na+ ions are in OCTAHEDRAL holes in a face-centered cubic lattice of Cl- ions.

The Sodium Chloride Lattice Many common salts have FCC arrangements of anions with cations in OCTAHEDRAL HOLES — e.g., salts such as CA = NaCl • FCC lattice of anions ----> 4 A-/unit cell • C+ in octahedral holes ---> 1 C+ at center + [12 edges • 1/4 C+ per edge] = 4 C+ per unit cell

Comparing NaCl and CsCl Even though their formulas have one cation and one anion, the lattices of CsCl and NaCl are different. The different lattices arise from the fact that a Cs+ ion is much larger than a Na+ ion.

Common Ionic Solids Titanium dioxide, TiO2 There are 2 net Ti4+ ions and 4 net O2- ions per unit cell.

Common Ionic Solids Zinc sulfide, ZnS The S2- ions are in TETRAHEDRAL holes in the Zn2+ FCC lattice. This gives 4 net Zn2+ ions and 4 net S2- ions.

Common Ionic Solids Fluorite or CaF2 FCC lattice of Ca2+ ions This gives 4 net Ca2+ ions. F- ions in all 8 tetrahedral holes. This gives 8 net F- ions.

Phase Diagrams

TRANSITIONS BETWEEN PHASES Section 13.10 Lines connect all conditions of T and P where EQUILIBRIUM exists between the phases on either side of the line. (At equilibrium particles move from liquid to gas as fast as they move from gas to liquid, for example.)

Phase Diagram for Water Liquid phase Solid phase Gas phase

Phase Equilibria — Water Solid-liquid Gas-Liquid Gas-Solid

Triple Point — Water At the TRIPLE POINT all three phases are in equilibrium.

Phases Diagrams— Important Points for Water T(˚C) P(mmHg) Normal boil point 100 760 Normal freeze point 0 760 Triple point 0.0098 4.58

Critical T and P As P and T increase, you finally reach the CRITICAL T and P Above critical T no liquid exists no matter how high the pressure.

Critical T and P COMPD Tc(oC) Pc(atm) H2O 374 218 CO2 31 73 CH4 -82 46 Freon-12 112 41 (CCl2F2) Notice that Tc and Pc depend on intermolecular forces.

Solid-Liquid Equilibria In any system, if you increase P the DENSITY will go up. Therefore — as P goes up, equilibrium favors phase with the larger density (or SMALLER volume/gram). Liquid H2O Solid H2O Density 1 g/cm3 0.917 g/cm3 cm3/gram 1 1.09

Solid-Liquid Equilibria Raising the pressure at constant T causes water to melt. The NEGATIVE SLOPE of the S/L line is unique to H2O. Almost everything else has positive slope.

Solid-Liquid Equilibria The behavior of water under pressure is an example of LE CHATELIER’S PRINCIPLE At Solid/Liquid equilibrium, raising P squeezes the solid. It responds by going to phase with greater density, i.e., the liquid phase. Solid-Liquid Equilibria

Solid-Vapor Equilibria At P < 4.58 mmHg and T < 0.0098 ˚C solid H2O can go directly to vapor. This process is called SUBLIMATION This is how a frost-free refrigerator works.