1. SolidsSolids Adapted from a presentation by Dr. Schroeder, Wayne State University

2. 2 Properties of Solids 1. Definite shape, definite volume 2. Particles are CLOSE together 3. STRONG IM forces 4.Often highly ordered, 5.Rigid, incompressible 1. Definite shape, definite volume 2. Particles are CLOSE together 3. STRONG IM forces 4.Often highly ordered, 5.Rigid, incompressible ZnS, zinc sulfide

3. 3 SOLIDS can be arranged into two categories: Crystalline Solids:Crystalline Solids: have a regular structure in which particles pack in a repeating pattern from one edge of the solid to another. Amorphous Solids:Amorphous Solids: “solids without form” have random structure and little long-range order. Includes glass and many plastics.

4. 4 CRYSTALLINE SOLIDS There are four types of crystalline solidsThere are four types of crystalline solids Classified on a basis of the bonding or attractive force holding them togetherClassified on a basis of the bonding or attractive force holding them together 1.Molecular solids 2.Covalent network solids 3.Ionic solids 4.Metallic solids

5. 5 1. Molecular Solids Composed of atoms or molecules held together by IMF’sComposed of atoms or molecules held together by IMF’s Relatively soft, low mp’s, bp’s, etc.Relatively soft, low mp’s, bp’s, etc. Water, carbon dioxide, NH 3, Iodine (I 2 ), sugar (C 12 H 22 O 11 ), and polyethylene are typical examples. Example: Dry ice (CO 2 ) sublimes at -78 o C. Strong intramolecular (covalent) bonds O==C==O Weak intermolecular forces - London O==C==O  -  +  - Symmetric molecule, nonpolar

6. 6 Molecular Solids (cont.): Example:Polyethylene (-CH 2 -CH 2 -) n Polyvinyl chloride (PVC) (-CH 2 -CHCl-) n or – H Cl H Cl H Cl – | | | | | | –.... C---C---C---C---C---C.... – | | | | | | NONPOLAR – H H H H H H London Forces

7. 7 2. COVALENT SOLIDS Form crystals that can be viewed as a single “giant” molecule held together by an endless number of covalent bonds. Diamond is an example of a covalent solid. Diamond is hard and difficult to melt (mp = 3,550 o C) because all bonds are equally strong. Also graphite, quartz, and asbestos.

8. 8Diamond Graphite

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10. 10 3. IONIC SOLIDS Are held together primarily by the strong force of attraction between oppositely charged ions (ionic bonds) Are typically hard, brittle, and nonconducting High mp’s and bp’s NaClCsFNaCl and CsF are typical examples. Note: the strength of the bond depends on the radii of the formative ions. That is, the bond becomes weaker as the ions become larger or the ratio changes away from 1:1

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12. 12 Common Ionic Solids Zinc sulfide, ZnSZinc sulfide, ZnS The S 2- ions are in TETRAHEDRAL holes in the Zn 2+ FCC lattice.The S 2- ions are in TETRAHEDRAL holes in the Zn 2+ FCC lattice. This gives 4 net Zn 2+ ions and 4 net S 2- ions.This gives 4 net Zn 2+ ions and 4 net S 2- ions.

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15. 15 4. METALLIC SOLIDS Malleable and ductile Held together by “metallic bonds” Have their valence electrons delocalized over many metal atoms. For this reason most metals are good conductors. –“sea of electrons” model –Jello with fruit Includes Au, Fe, Al, etc.

16. 16 4. METALLIC SOLIDS Atom “core” e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- Delocalized valence electrons (move around)

17. 17 Types of Crysatalline Solids TYPEEXAMPLEFORCE 1. Molecular Ice, I 2 Dipole London 2. Network DiamondExtended Graphitecovalent 3. Ionic NaCl, CaF 2, ZnSIon-ion 4. Metallic Na, FeMetallic TYPEEXAMPLEFORCE 1. Molecular Ice, I 2 Dipole London 2. Network DiamondExtended Graphitecovalent 3. Ionic NaCl, CaF 2, ZnSIon-ion 4. Metallic Na, FeMetallic

18. 18 Amorphous Solids No regular geometric patternNo regular geometric pattern More “jumbled up”More “jumbled up” Typically long chains of molecules that get tangled up togetherTypically long chains of molecules that get tangled up together Classified on a basis of the bonding or attractive force holding them togetherClassified on a basis of the bonding or attractive force holding them together Held together by IMF’sHeld together by IMF’s Examples: waxes, asphalt, many plasticsExamples: waxes, asphalt, many plastics