Ch13_Solids-1

Ch13_Solids-1 - Types of Solids Types of Solids Metallic...

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Unformatted text preview: Types of Solids Types of Solids Metallic and Ionic Solids Metallic and Ionic Solids Tablle 13..6 Tab e 13 6 Sectton 13..4 Sec iion 13 4 TYPE TYPE Ionic Ionic EXAMPLE EXAMPLE NaCl, CaF 2,, ZnS NaCl CaF 2 ZnS aCl, Metallic Metallic Na, Fe Na, Fe Molecular Ice, II2 Molecular Ice, 2 Network Network Network Solids Diamond Diamond Graphite Graphite Network Solids Network Solids FORCE FORCE Ion-ion Ion-ion Metallic Metallic Dipole Dipole Ind. dipole Ind. Extended Extended covalent covalent Properties of Solids Properties of Solids Diamond Graphite Crystal Lattices Crystal Lattices 1. Molecules, atoms or 1. Molecules, atoms or ions locked into a ions locked into a Regular 3-D arrangements of equivalent Regular 3-D arrangements of equivalent LATTICE POINTS in space. LATTICE POINTS in space. 2. Particles are CLOSE 2. Particles are CLOSE together together 3. STRONG IM forces 3. STRONG IM forces 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 CRYSTAL LATTICE CRYSTAL A comparison of diamond (pure carbon) with silicon. only concerned with CUBIC .. only concerned with CUBIC 4. Highly ordered, rigid, 4. Highly ordered, rigid, incompressible incompressible ZnS, zinc sulfide Page 1 Cubic Unit Cells Cubic Unit Cells All angles are 90 degrees Cubic Unit Cells of Metals Cubic Unit Cells of Metals Figurre 13..28 Figu e 13 28 Simple cubic (SC) Bodycentered cubic (BCC) All sides equal length Simple Cubic Unit Cell Simple Cubic Unit Cell Figurre 13..28 Figu e 13 28 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 plus atom 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 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. Simple Ionic Compounds 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. Number of Atoms per Unit Cell Number of Atoms per Unit Cell Unit Cell Type Unit Cell Type SC SC Net Number Atoms Net Number Atoms 1 1 BCC BCC FCC FCC 2 2 4 4 Simple Ionic Compounds Simple Ionic Compounds Salts with formula MX can have SC structure — but not salts with formula MX 2 or M 2X Page 3 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 with Cl- in the center. Construction of NaCl Construction of NaCl We begin with a cube of Cl- ions. Add more Cl- ions in the cube faces, and then add Na+ ion in the octahedral holes. 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 Na+ ions are in OCTAHEDRAL holes in a face-centered cubic lattice of Clions. Comparing NaCl and CsCl 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. • 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 Common Ionic Solids Common Ionic Solids Titanium dioxide, TiO2 There are 2 net Ti4+ ions and 4 2- ions net O 2- ions per unit cell. Page 4 Common Ionic Solids Common Ionic Solids • Zinc sulfide, ZnS • The S2- ions are in TETRAHEDRAL holes in the Zn 2+ FCC lattice. • This gives 4 net Zn2+ ions and 4 net S2- ions. 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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