CH 102 1st Edition Lecture 5 Outline of Current Lecture I. Molecular Solids II. Ionic SolidsIII. Network Covalent SolidsIV. The Graphite Structure: A Two-Dimensional NetworkV. The Diamond Structure: A Three-Dimensional NetworkVI. Buckminsterfullerene: BuckyballVII. NanotubesCurrent LectureI. Molecular Solidsa. The lattice sites are occupied by molecules.i. CO2, H2O, C12H22O11b. The molecules are held together by intermolecular attractive forces.i. Dispersion forces, dipole–dipole attractions, and H bondsc. Because the attractive forces are weak, they tend to have low melting points.i. Generally < 300 °CII. Ionic Solidsa. Lattice sites are occupied by ions.b. They are held together by attractions between oppositely charged ions.i. Nondirectionalii. Therefore, every cation attracts all anions around it, and vice versa.c. The coordination number represents the number of close cation–anion interactions in the crystal. i. The higher the coordination number, the more stable the solid .1. Lowers the potential energy of the solidd. The coordination number depends on the relative sizes of the cations and anions that maintain charge balance.i. Generally, anions are larger than cations.1. The number of anions that can surround the cation is limited by the size of the cation.2. The closer in size the ions are, the higher the coordination number.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.e. Structure of Ionic Solids: Cesium Chloridei. Coordination number = 81. ⅛ of each Cl– (184 pm) inside the unit cellii. Whole Cs+ (167 pm) inside the unit cell1. Cubic hole = hole in simple cubic arrangement of Cl– ionsiii. Cs:Cl = 1:(8 × ⅛); therefore the formula is CsCl.f. The Structure of Ionic Solids: Rock Salti. Coordination number = 6ii. Cl– ions (181 pm) in a face-centered cubic arrangement.1. ⅛ of each corner Cl– inside the unit cell2. ½ of each face Cl– inside the unit celliii. Na+ (97 pm) in holes between Cl– 1. Octahedral holes2. 1 in center of unit cell3. 1 whole particle in every octahedral hole4. ¼ of each edge Na+ inside the unit celliv. Na:Cl = (¼ × 12) + 1:(⅛ × 8) + (½ × 6) = 4:4 = 1:1 1. Therefore, the formula is NaCl.g. The Structure of Ionic Solids: Zinc Blendei. Coordination number = 4ii. S2– ions (184 pm) in a face-centered cubic arrangement1. ⅛ of each corner S2– inside the unit cell2. ½ of each face S2– inside the unit celliii. Each Zn2+ (74 pm) in holes between S2– 1. Tetrahedral holes2. 1 whole particle in ½ the holesiv. Zn:S = (4 × 1):(⅛ × 8) + (½ × 6) = 4:4 = 1:1 1. Therefore, the formula is ZnS.III. Network Covalent Solidsa. Atoms attach to their nearest neighbors by covalent bonds.b. Because of the directionality of the covalent bonds, these do not tend to form closest-packed arrangements in the crystal.c. Because of the strength of the covalent bonds, these have very high melting points.i. Generally > 1000 °Cd. Dimensionality of the network affects other physical properties.IV. The Graphite Structure: A Two-Dimensional Networka. In graphite, the carbon atoms in a sheet are covalently bonded together.i. Forming six-member flat rings fused together1. Similar to benzene2. Bond length = 142 pmii. sp2 1. Each C has three sigma bonds and one pi bond.iii. Trigonal-planar geometryiv. Each sheet a giant moleculeb. The sheets are then stacked and held together by dispersion forces.i. Sheets are 341 pm apart.c. Properties of Graphitei. Hexagonal crystalsii. High melting point, ~3800 °C1. Need to overcome some covalent bondingiii. Slippery feel1. Because there are only dispersion forces holding the sheets together, they can slide past each other.a. Glide planes2. Lubricantsiv. Electrical conductor1. Parallel to sheetsv. Thermal insulatorvi. Chemically very nonreactiveV. The Diamond Structure: A Three-Dimensional Networka. Each of the carbon atoms in a diamond has four covalent bonds to surrounding atoms.i. sp3ii. Tetrahedral geometryb. This effectively makes each crystal one giant molecule held together by covalent bonds.i. You can follow a path of covalent bonds from any atom to every other atom.c. Properties of Diamondi. Very high melting point, ~3800 °C1. Need to overcome some covalent bondsii. Very rigid1. Due to the directionality of the covalent bondsiii. Very hard1. Due to the strong covalent bonds holding the atoms in position2. Used as abrasivesiv. Electrical insulatorv. Thermal conductor1. Best known vi. Chemically very nonreactiveVI. Buckminsterfullerene: Buckyballa. A form of carbon occurs as soccer-ball-shaped clusters of 60 carbon atoms (C60).i. The atoms form five- and six-membered carbon rings wrapped into a 20-sided icosahedral structure.b. The compound is named buckminsterfullerene. i. After R. Buckminster Fuller, a twentieth-century engineer and architect who advocated the construction of buildings using a structurally strong geodesic dome shape that he patentedc. Other carbon clusters have been identified similar to C60 that contain from 36 to over 100 carbon atoms.i. As a class, these carbon clusters are called fullerenes and nicknamed buckyballs. d. Properties:i. At room temperature, fullerenes are black solids.ii. The individual clusters are held to one another by dispersion forces. iii. Fullerenes are somewhat soluble in nonpolar solvents.iv. Some fullerenes are colored when in solution.VII.