Chapter 16 Liquids and Solids Chapter 16 Slide 1 of 87
Chapter Preview Intramolecular forces determine such molecular properties as molecular geometries and dipole moments. Intermolecular forces determine the macroscopic physical properties of liquids and solids. Three states of matter: solids, liquids, and gases. In gases and liquids, motion is mainly translational. In solids, motion is mainly vibrational. This chapter describes changes from one state of matter to another and explores the types of intermolecular forces that underlie the physical properties of substances. Chapter 16 Slide 2 of 87
Table 2.11 Chapter 16 Slide 3 of 87
States of Matter Compared Chapter 16 Slide 4 of 87
Dipole-Dipole Forces Dipole-dipole forces arise when permanent dipoles align themselves with the positive end of one dipole directed toward the negative ends of neighboring dipoles. When molecules come close to one another, repulsions occur between like-charged regions of dipoles. A permanent dipole in one molecule can induce a dipole in a neighboring molecule, giving rise to a dipole-induced dipole force. The more polar a molecule, the more pronounced is the effect of dipole-dipole forces on physical properties. Chapter 16 Slide 5 of 87
Dipole-Dipole Interactions d µ 1 r Dipole moment µ = δ d µ 2 E = - 2(µ 1 µ 2 )/4πεr 3
Dispersion Forces A dispersion force is the force of attraction between an instantaneous dipole and an induced dipole. Also called a London force after Fritz London who offered a theoretical explanation of these forces in 1928. The polarizability of an atom or molecule is a measure of the ease with which electron charge density is distorted by an external electrical field. The greater the polarizability of molecules, the stronger the intermolecular forces between them. Chapter 16 Slide 7 of 87
Dispersion Forces Illustrated r µ µ E = - 2(µ 2 α)/r 6 Mean instantaneous dipole polarizability
Predicting Physical Properties of Molecular Substances Dispersion forces become stronger with increasing molar mass and elongation of molecules. In comparing nonpolar substances, molar mass and molecular shape are the essential factors. Dipole-dipole and dipole-induced dipole forces are found in polar substances. The more polar the substance, the greater the intermolecular force is expected to be. Because they occur in all molecular substances, dispersion forces must always be considered. Often they predominate. Chapter 16 Slide 9 of 87
Molecular Shape and Polarizability Chapter 16 Slide 10 of 87
Chapter 16 Slide 11 of 87
Effect of Molecular Weight & Dipole Moment Compound M.W. Dipole (D) moment b.p. ( 0 C) CH 3 Cl 50.5 1.87-24.2 CH 2 Cl 2 84.9 1.60 +40 CHClF 2 86.5 1.42-40.8 CF 4 88.0 0-129 CCl 4 153.8 0 76.5 Chapter 16 Slide 12 of 87
Hydrogen Bonds A hydrogen bond is an intermolecular force in which a hydrogen atom covalently bonded to a non-metal atom in one molecule is simultaneously attracted to a non-metal atom of a neighboring molecule. The strongest hydrogen bonds are formed if the non-metal atoms are small and highly electronegative. Usually occurs with nitrogen, oxygen, and fluorine atoms. Dotted lines are used to represent hydrogen bonds. X H Y X, Y = F, O, N, Cl, S (highly electronegative elements) Chapter 16 Slide 13 of 87
Hydrogen Bonds in Water
Hydrogen Bonding in Ice Chapter 16 Slide 15 of 87
Solid water is less dense than liquid water due to hydrogen bonding. Chapter 16 Slide 16 of 87
HF Chapter 16 Slide 17 of 87
Hydrogen bonding is also the reason for the unusually high boiling point of water. Chapter 16 Slide 18 of 87
Figure 25.19 Chapter 16 Slide 19 of 87
Intermolecular Forces in a Liquid Surface tension Chapter 16 Slide 20 of 87
Adhesive and Cohesive Forces Chapter 16 Slide 21 of 87
Meniscus Formation Chapter 16 Slide 22 of 87
Vaporization and Condensation Liquid Vaporization Condensation Vapor Vaporization is the conversion of a liquid to a gas. The enthalpy of vaporization ( H vapn ) is the quantity of heat that must be absorbed to vaporize a given amount of liquid at a constant temperature. Condensation ( H condn ) is the change of a gas to a liquid. H condn = - H vapn Chapter 16 Slide 23 of 87
Some Enthalpies of Vaporization Chapter 16 Slide 24 of 87
Vapor Pressure The vapor pressure of a liquid is the partial pressure exerted by the vapor when it is in dynamic equilibrium with a liquid at a constant temperature. The vapor pressures of liquids increases with temperature. A vapor pressure curve is a graph of vapor pressure as a function of temperature. Chapter 16 Slide 25 of 87
Liquid-Vapor Equilibrium Chapter 16 Slide 26 of 87
Vapor Pressure Of Water Chapter 16 Slide 27 of 87
Vapor Pressure Curves a) Carbon disulfide: CS 2 b) Methanol: CH 3 OH c) Ethanol: CH 3 CH 2 OH d) Water: H 2 O e) Aniline: C 6 H 5 NH 2 The temperature of the line at P= 760 mmhg with a vapor pressure curve is the normal boiling point. Chapter 16 Slide 28 of 87
Vapor Pressure as a Function of Temperature Clausius-Clapeyron equation: ln(p 2 /P 1 ) = ( H vap /R)(1/T 1-1/T 2 ) where, H vap = enthalpy of vaporization Chapter 16 Slide 29 of 87
Generalized Phase Diagram Fusion curve Sublimation curve Vapor Pressure curve Triple point Critical point Supercritical fluid Chapter 16 Slide 30 of 87
Phase Diagram For H 2 O normal melting point normal boiling point Chapter 16 Slide 31 of 87
Phase Diagram For H 2 O normal melting point normal boiling point Chapter 16 Slide 32 of 87
Boiling Point and Critical Point The boiling point of a liquid is the temperature at which its vapor pressure becomes equal to the external pressure. The normal boiling point is the boiling point at 1 atm. The critical temperature, T c, is the highest temperature at which a liquid and vapor can co-exist in equilibrium as physically distinct states of matter. The critical pressure, P c, is the vapor pressure at the critical temperature. The condition corresponding to a temperature of T c and a pressure of P c is called the critical point. Chapter 16 Slide 33 of 87
The Critical Point Chapter 16 Slide 34 of 87
Phase Changes Involving Solids The conversion of a solid to a liquid is called melting, or fusion, and the temperature at which a solid melts is its melting point. The enthalpy of fusion, H fusion, is the quantity of heat required to melt a given amount of solid. Sublimation is the process of a molecules passing directly from the solid to the vapor state. Enthalpy of sublimation, H subln, is the sum of the enthalpies of fusion and vaporization. The triple point is the point at which the vapor pressure curve and the sublimation curve meet. Chapter 16 Slide 35 of 87
Phase Diagram For CO 2 Sublimation of dry ice Chapter 16 Slide 36 of 87
Critical Temperature and Pressure of Various Substances Chapter 16 Slide 37 of 87
Some Enthalpies of Fusion Chapter 16 Slide 38 of 87
Cooling Curve For Water Expected m.p. supercooled Crystallization begins Chapter 16 Slide 39 of 87
Heating Curve For H 2 O Chapter 16 Slide 40 of 87
Phase Diagram For HgI 2 25 0 C Chapter 16 Slide 41 of 87
Phase Diagram of Carbon Chapter 16 Slide 42 of 87
Some Characteristics of Crystalline Solids Chapter 16 Slide 43 of 87
Network Covalent Solids These substances contain a network of covalent bonds that extend throughout a crystalline solid, holding it firmly together. The allotropes of carbon provide a good example 1. Diamond has each carbon bonded to four other carbons in a tetrahedral arrangement using sp 3 hybridization. 2. Graphite has each carbon bonded to three other carbons in the same plane using sp 2 hybridization. 3. Fullerenes are roughly spherical collections of carbon atoms in the shape of a soccer ball. Chapter 16 Slide 44 of 87
Crystal Structure of Diamond Covalent bond Chapter 16 Slide 45 of 87
Crystal Structure of Graphite Covalent bond van der Waals force Chapter 16 Slide 46 of 87
Structure of a Buckyball Covalent bond Chapter 16 Slide 47 of 87
Carbon Nano-tube Covalent bond Chapter 16 Slide 48 of 87
Experimental Determination of Crystal Structures Bragg s Law 2 d sinθ = n λ Chapter 16 Slide 49 of 87
William Lawrence Bragg and William Henry Bragg Chapter 16 Slide 50 of 87
X-Ray Diffraction Image & Pattern Single crystal Powder Chapter 16 Slide 51 of 87
Crystal Lattices To describe crystals, three-dimensional views must be used. The repeating unit of the lattice is called the unit cell. The simple cubic cell (primitive cubic) is the simplest unit cell and has structural particles centered only at its corners. The body-centered cubic (bcc) structure has an additional structural particle at the center of the cube. The face-centered cubic (fcc) structure has an additional structural particle at the center of each face. Chapter 16 Slide 52 of 87
14 Bravais Lattice Chapter 16 Slide 53 of 87
Unit Cells In Cubic Crystal Structures simple cubic (primitive cubic) bcc fcc Chapter 16 Slide 54 of 87
Primitive cubic, Body-centered cubic, Face-centered cubic Primitive cubic Body-centered cubic Face-centered cubic Chapter 16 Slide 55 of 87
Occupancies per Unit Cells Primitive cubic: a = 2r 1 atom/unit cell occupancy = [4/3(πr 3 )]/a 3 = [4/3(πr 3 )]/(2r) 3 = 0.52 = 52% Body-centered cubic: a = 4r/(3) 1/2 2 atom/unit cell occupancy = 2 x [4/3(πr 3 )]/a 3 = 2 x [4/3(πr 3 )]/[4r/(3) 1/2 ] 3 = 0.68 = 68% Face-centered cubic: a = (8) 1/2 r 4 atom/unit cell occupancy = 4 x [4/3(πr 3 )]/a 3 = 4 x [4/3(πr 3 )]/[(8) 1/2 r] 3 = 0.74 = 74% Closest packed Chapter 16 Slide 56 of 87
Using desity to identify structure The atomic radius of copper is 128 pm, mass number is 63.54, and the density of copper is 8.93g/cm 3. Is copper metal close packed? Density = M/V, V= M/D The volume of a Cu atom occupied in the lattice = 63.54g/mol 8.93g/cm 3 6.02 x 10 23 atom/mol = 1.18 x 10-23 cm 3 /atom = 1.18 x 10 7 pm 3 /atom Occupancy = [4/3(πr 3 )]/[1.18 x 10 7 ] = [4/3 π( 128 3 )]/[1.18 x 10 7 ] = 0.744 = 74.4% Close-packed structure Chapter 16 Slide 57 of 87
Crystal Structures of Metals Chapter 16 Slide 58 of 87
Closest packed a ab aba unoccupied holes abc Chapter 16 Slide 59 of 87
Closest packed abab abcabc = Face-centered cubic Chapter 16 Slide 60 of 87
Close-packing of Spheres in Three Dimensions Chapter 16 Slide 61 of 87
Close Packed Structures First two layers of spheres are close-packed. Tetrahedral holes are located above a sphere in the bottom layer. Octahedral holes are located above a void in the bottom layer. Hexagonal close-packed (hcp) arrangements occur when the third layer covers the tetrahedral holes. These produce two-layer repeating units. ABABAB.. Cubic close-packed (ccp) arrangements occur when the third layer covers the octahedral holes. These produce three-layer repeating units. ABCABC. Chapter 16 Slide 62 of 87
Ionic Bonds in Ionic Solids There are simply inter-ionic attractions in an ionic solid. Lattice energy is a measure of the strength of inter-ionic attraction. The attractive force between a pair of oppositely charged ions increases as the charges on the ions increase and as the ionic radii decrease. Lattice energies increase accordingly. E = (Z + Z - )/4πεr Chapter 16 Slide 63 of 87
Interionic Forces of Attraction E = (Z + Z - )/4πεr Chapter 16 Slide 64 of 87
A Born-Haber Cycle to Calculate Lattice Energy NaCl(s) U Na + (g) + Cl - (g) Η f 0 (NaCl) IE(Na) -EA(Cl) Na(s) + 1/2Cl 2 (g) Η sublimation (Na) 1/2D(Cl-Cl) Na(g) + Cl(g) lattice energy U = - Η f 0 (NaCl) + Η sublimation (Na) + 1/2D(Cl-Cl) + IE(Na) - EA(Cl) = (+411 +107 +122 + 496 349) kj/mol = +787 kj/mol Chapter 16 Slide 65 of 87
Ionic Crystal Structures Ionic crystals have two different types of structural units - cations and anions. The cations and anions are different sizes. Smaller cations can fill the voids between the larger anions. Radii ratio: Tetrahedral hole 0.225 < r c /r a < 0.414 Octahedral hole 0.414 < r c /r a < 0.732 Cubic hole r c /r a > 0.732 Chapter 16 Slide 66 of 87
Tetrahedral, Octahedral and Cubic holes Tetrahedral holes Octahedral holes Cubic holes Close packed structure Chapter 16 Slide 67 of 87
Radius ratio r h /r = 0.414 r h /r = 0.225 r h /r = 0.156 Chapter 16 Slide 68 of 87
Unit Cell of Rock-Salt (Sodium Chloride) Coord. #: Na + : 6; Cl - : 6 atom/ unit cell Na: Cl= 4: 4 = 1: 1 NaCl Cl - at fcc Na + at O h holes Chapter 16 Slide 69 of 87
Unit Cell of Cesium Chloride Coord. #: Cs + : 8; Cl - : 8 atom/ unit cell Cs: Cl= 1: 1 CsCl Cl - at primitive cubic Cs + at Cubic holes Chapter 16 Slide 70 of 87
Unit Cell of Cubic Zinc Sulfide (Sphalerite or Zinc blende) Coord. #: Zn 2+ : 4; S 2- : 4 atom/ unit cell Zn: S = 4: 4 = 1: 1 ZnS S 2- at fcc Zn 2+ at ½ Td holes Chapter 16 Slide 71 of 87
Quartz SiO 2 Si 4+ at fcc and ½ Td holes O 2- in between two Si Chapter 16 Slide 72 of 87
Si x O y Chapter 16 Slide 73 of 87
Table 16.4 Chapter 16 Slide 74 of 87
Unit Cell of Fluorite Structure (Calcium Fluoride) Coord. #: Ca 2+ : 8; F - : 4 atom/ unit cell Ca: F= 4: 8 = 1: 2 Ca 2+ at fcc F - at Td holes Chapter 16 Slide 75 of 87
Unit Cell of Rutile TiO 2 Coord. #: Ti: 6; O: 3 atom/ unit cell Ti: O= 2: 4 = 1: 2 O 2- at hcp Ti 4+ at ½ O h holes Chapter 16 Slide 76 of 87
Unit Cell of Perovskite CaTiO 3 A II B IV O 3 A III B III O 3 A and O together at ccp B at 1/4 O h holes Coord. #: A: 12; B: 6 atom/ unit cell A: B: O= 1: 1: 3 Chapter 16 Slide 77 of 87
Unit Cell of Spinel MgAl 2 O 4 Normal Spinel A II [B III ] 2 O 4,A IV [B II ] 2 O 4,A VI [B I ] 2 O 4 e.g. NiCr 2 O 4, Co 3 O 4, Mn 3 O 4 O 2- at fcc A at 1/8 T d holes B at 1/2 O h holes Inverse Spinel B[AB]O 4 e.g. Fe 3 O 4 Chapter 16 Slide 78 of 87
Unit Cell of YBa 2 Cu 3 O 7 Chapter 16 Slide 79 of 87
Temperature vs Resistance Chapter 16 Slide 80 of 87
Band Theory This is a quantum-mechanical treatment of bonding in metals. The spacing between energy levels is so minute in metals that the levels essentially merge into a band. When the band is occupied by valence electrons, it is called a valence band. A partially filled or low lying empty band of energy levels, which is required for electrical conductivity, is a conduction band. Band theory provides a good explanation of metallic luster and metallic colors. Chapter 16 Slide 81 of 87
Energy Band Antibonding bonding Chapter 16 Slide 82 of 87
The 2s Band in Lithium Metal Anti-bonding Conduction band e- e- Bonding Valence band Chapter 16 Slide 83 of 87
Band Overlap in Magnesium Conduction band Valence band Chapter 16 Slide 84 of 87
Band Structure of Insulators and Semiconductors Chapter 16 Slide 85 of 87
Table 3.1 Chapter 16 Slide 86 of 87
p-and n-type Semiconductors e- e- e- e- e- e- e.g. Si doped with P or As e.g. Si doped with Ga or In Chapter 16 Slide 87 of 87
p- n junction excess hole Excess electron No current flows (reverse bias) Current flows (forward bias) Chapter 16 Slide 88 of 87