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Unformatted text preview: Metallic and Ionic Solids Metallic and Ionic Solids
Section 13.4 Section 13.4 Types of Solids Types of Solids
Table 13.6 Table 13.6 Network Solids Network Solids
Diamond TYPE TYPE Ionic Ionic EXAMPLE EXAMPLE NaCl, CaF 2,, ZnS NaCl, CaF 2 ZnS NaCl, FORCE FORCE Ion-ion Ion-ion Metallic Metallic Dipole Dipole Ind. dipole Ind. Ind. Extended Extended covalent covalent Metallic Na, Fe Metallic Na, Fe Na, Molecular Ice, II2 Molecular Ice, 2 Network Network Diamond Diamond Graphite Graphite Graphite Network Solids Properties of Solids Properties of Solids
1. Molecules, atoms or 1. Molecules, atoms or ions locked into a ions locked into a Crystal Lattices Crystal Lattices
Regular 3-D arrangements of equivalent Regular 3-D arrangements of equivalent LATTICE POINTS in space. LATTICE POINTS in space. The lattice points define UNIT CELLS ,, The lattice points define UNIT the smallest repeating internal unit that has the 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 are There are 7 basic crystal systems, but we are only concerned with CUBIC .. only concerned with CUBIC CRYSTAL LATTICE CRYSTAL 2. Particles are CLOSE 2. Particles are CLOSE together together 3. STRONG IM forces 3. STRONG IM forces A comparison of diamond (pure carbon) with silicon. 4. Highly ordered, rigid, 4. Highly ordered, rigid, incompressible incompressible
ZnS, zinc sulfide ZnS, Page 1 Cubic Unit Cells Cubic Unit Cells
All angles are 90 degrees Cubic Unit Cells of Metals Cubic Unit Cells of Metals
Figure 13.28 Figure 13.28 Simple Cubic Unit Cell Simple Cubic Unit Cell
Figure 13.28 Figure 13.28 Simple cubic (SC) Bodycentered cubic (BCC) All sides equal length Facecentered cubic (FCC) • Simple cubic unit cell. • Note that each atom is at a corner of a unit cell and is shared among 8 unit cells. Body-Centered Cubic Unit Cell Body-Centered Cubic Unit Cell Face Centered Cubic Face Centered Cubic Unit Cell Unit Cell
Atom at each cube corner plus atom in each Atom at each cube corner cube face. cube face. Crystal Lattices— Crystal Lattices— Packing of Atoms or Ions Packing of Atoms or Ions
Assume atoms are Assume atoms are hard spheres and hard spheres and that crystals are that crystals are built by PACKING built by PACKING of these spheres of these spheres as efficiently as as efficiently as possible. possible. FCC is more FCC is more efficient than efficient than either BC or SC. either BC or SC.
See Closer Look, pp. 622-623 pp. Page 2 Crystal Lattices— Crystal Lattices— Packing of Atoms or Ions Packing of Atoms or Ions
Packing of C 60 molecules. They are arranged at the lattice points of a FCC lattice. Number of Atoms per Unit Cell Number of Atoms per Unit Cell
Unit Cell Type Unit Cell Type SC SC BCC BCC FCC FCC Net Number Atoms Net Number Atoms 1 1 2 2 4 4 Simple Ionic Compounds 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 ions with Cl- in the center. in Simple Ionic Compounds Simple Ionic Compounds
CsCl has a SC lattice of Cs+ ions with Cl- in the ions in center. 1 unit cell has 1 Cl- ion ion plus (8 corners)(1/8 Cs + per per corner) = 1 net Cs + ion. ion. Simple Ionic Compounds Simple Ionic Compounds Salts with formula MX can have SC structure — but not salts with formula MX 2 or or M 2X Construction of NaCl Construction of
We begin with a cube of Cl- ions. Add more Cl- ions in ions. ions the cube faces, and then add Na+ ion in the octahedral ion holes. Page 3 The Sodium Chloride Lattice The Sodium Chloride Lattice The Sodium Chloride Lattice The Sodium Chloride Lattice
Many common salts have FCC arrangements of anions with cations in OCTAHEDRAL OCTAHEDRAL HOLES — e.g., salts such as CA = NaCl e.g., • FCC lattice of anions ----> 4 A -/unit cell • C+ in octahedral holes ---> 1 C + at center in at + [12 edges 1/4 C + per edge] per = 4 C+ per unit cell per Na+ ions are in ions OCTAHEDRAL holes in a face-centered cubic lattice of Clions. Comparing NaCl and CsCl Comparing NaCl and CsCl Common Ionic Solids Common Ionic Solids
Titanium dioxide, TiO2 There are 2 net Ti4+ ions and 4 ions net O 2- ions per ions unit cell. Common Ionic Solids Common Ionic Solids
• Zinc sulfide, ZnS • The S2- ions are in ions TETRAHEDRAL holes in the Zn 2+ FCC lattice. • This gives 4 net Zn2+ ions and 4 ions net S2- ions. ions. • 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. Page 4 Common Ionic Solids Common Ionic Solids
• Fluorite or CaF2 • FCC lattice of Ca 2+ ions • This gives 4 net Ca2+ ions. • F- ions in all 8 tetrahedral holes. • This gives 8 net F ions. Page 5 ...
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This note was uploaded on 01/11/2011 for the course ENGINEERIN MAE 107 taught by Professor Pozikrizdis during the Fall '08 term at San Diego.
- Fall '08