Intermolecular Forces and Liquids and Solids Chapter 12 Copyright © The McGraw-Hill Companies, Inc.  Permission required for reproduction or display.

Homework pages 398-401 1-7, 9-16, 18, 21, 29, 30, 35-39, 41, 42, 51, 53-56, 59-62, 65-67, 72, 82, 86-88, 92, 94, 95, 98, 100

A phase is a homogeneous part of the system in contact with other parts of the system but separated from them by a well-defined boundary. 2 Phases Solid phase - ice Liquid phase - water

Intermolecular Forces Intermolecular forces are attractive forces between molecules. Intramolecular forces hold atoms together in a molecule. Intermolecular vs Intramolecular 41 kJ to vaporize 1 mole of water (inter) 930 kJ to break all O-H bonds in 1 mole of water (intra) “Measure” of intermolecular force boiling point melting point DHvap DHfus DHsub Generally, intermolecular forces are much weaker than intramolecular forces.

Intermolecular Forces Dipole-Dipole Forces Attractive forces between polar molecules Orientation of Polar Molecules in a Solid 11.2

Intermolecular Forces Ion-Dipole Forces Attractive forces between an ion and a polar molecule Ion-Dipole Interaction 11.2

Dispersion (London) force - arise as a result of temporary dipoles induced in the molecules or atoms. - act between all molecules - only force between nonpolar molecules and noble gas atoms - strength depends primarily on size of molecule, very weak for small molec. but fairly strong for large ones. (Shape plays a role too.)

Intermolecular Forces Dispersion Forces Continued Polarizability is the ease with which the electron distribution in the atom or molecule can be distorted. Polarizability increases with: greater number of electrons more diffuse electron cloud Dispersion forces usually increase with molar mass. 11.2

What type(s) of intermolecular forces exist between each of the following molecules? HBr HBr is a polar molecule: dipole-dipole forces. There are also dispersion forces between HBr molecules. CH4 CH4 is nonpolar: dispersion forces. S O CO2 SO2 11.2

Intermolecular Forces Hydrogen Bond The hydrogen bond is a special dipole-dipole interaction between the hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom. A H … B or A & B are N, O, or F 11.2

Why is the hydrogen bond considered a “special” dipole-dipole interaction? Decreasing molar mass Decreasing boiling point 11.2

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Dispersion forces affect all molecules. H bonds are found between two molecules of the same kind only if they contain an O-H, N-H, or F-H bond. (water and acetone) These forces only affect molecular substances.

Test on chapters 12 & 13 – EH Assignment Due Unit 14 Liquids and Solids Mininum score Sec 1 Changes of Physical State 90 Sec 2 Types of Bonding in Solids Sec 3 Crystalline Solids Optional Sec 4 Intermolecular Forces Sec 5 Vapor Pressure Sec 6 Phase Diagrams Test on chapters 12 & 13 –

Strong intermolecular forces Properties of Liquids Surface tension is the amount of energy required to stretch or increase the surface of a liquid by a unit area. Strong intermolecular forces High surface tension 11.3

Properties of Liquids Cohesion is the intermolecular attraction between like molecules Adhesion is an attraction between unlike molecules Adhesion Cohesion 11.3

Strong intermolecular forces Properties of Liquids Viscosity is a measure of a fluid’s resistance to flow. Strong intermolecular forces High viscosity Note glycerol 11.3

Predicting the Type and Relative Strength of Intermolecular Forces Problem: Identify the dominant intermolecular force that is present in each of the following substances, and select the substance with the higher boiling point in each pair: NCl3 or BeF2 b) CH3Cl or CH3OH c) CH3CH2OH or C2H4(OH)2 d) Butane, C4H10 or Pentane, C5H12

The Uniqueness of Water Water is an excellent solvent for many ionic compounds and for many molecules capable of forming hydrogen bonds with water. Water has a very high boiling point for such a small molecule. It also has a high specific heat, surface tension, heat of vaporization, etc. The solid form of water is less dense than the liquid form. Ice floats. All due to strong H bonds.

Ice is less dense than water Water is a Unique Substance Maximum Density 40C Density of Water Ice is less dense than water 11.3

The Solid State 1. Crystalline solids have well defined shapes because their particles (atoms, molecules, ions) occur in an orderly arrangement. They have sharp melting points.

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The Solid State 2. Amorphous solids such as glass have poorly defined shapes because their particles do not occur in an orderly arrangement. They don’t melt sharply, but gradually soften over a range of temperature.

Skip section 12.4 11.4

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Shared by 8 unit cells Shared by 2 unit cells 11.4

1 atom/unit cell 2 atoms/unit cell 4 atoms/unit cell (8 x 1/8 = 1) (8 x 1/8 + 1 = 2) (8 x 1/8 + 6 x 1/2 = 4) 11.4

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Types of Solids Ionic Crystals Lattice points occupied by cations and anions Held together by electrostatic attraction Hard, brittle, high melting point Poor conductor of heat and electricity CsCl ZnS CaF2 11.6

Types of Solids Covalent Crystals (Network Covalent or Macromolecular) Lattice points occupied by atoms Held together by covalent bonds Hard, high melting point Poor conductor of heat and electricity carbon atoms diamond graphite 11.6

Types of Solids Molecular Crystals Lattice points occupied by molecules Held together by intermolecular forces Soft, low melting point Poor conductor of heat and electricity 11.6

Cross Section of a Metallic Crystal Types of Solids Metallic Crystals Lattice points occupied by metal atoms Held together by metallic bonds Soft to hard, low to high melting point Good conductors of heat and electricity Cross Section of a Metallic Crystal nucleus & inner shell e- mobile “sea” of e- 11.6

Other examples of covalent are BN, Si, and SiC Types of Crystals Other examples of covalent are BN, Si, and SiC 11.6

An amorphous solid does not possess a well-defined arrangement and long-range molecular order. A glass is an optically transparent fusion product of inorganic materials that has cooled to a rigid state without crystallizing Crystalline quartz (SiO2) Non-crystalline quartz glass 11.7

Not all solids fall into one of the four classes just discussed Not all solids fall into one of the four classes just discussed. Many minerals have a structure consisting of a network covalent structure that has a negative charge. Metal cations form ionic bonds to this network covalent anion. The silicates are the largest, the most interesting and the most complicated class of minerals by far. Approximately 30% of all minerals are silicates and some geologists estimate that 90% of the Earth's crust is made up of silicates. With oxygen and silicon the two most abundant elements in the earth's crust silicates abundance is no real surprise. The basic chemical unit of silicates is the (SiO4) tetrahedron shaped anionic group with a negative four charge (-4). The oxygens can bond to another silicon atom and therefore linking one (SiO4) tetrahedron to another and another, etc.. The complicated structures that these silicate tetrahedrons form is truly amazing. They can form as single units, double units, chains, sheets, rings and framework structures. The different ways that the silicate tetrahedrons combine is what makes the Silicate Class the largest, the most interesting and the most complicated class of minerals. KAlSi3O8 is a feldspar

Sample problems What kinds of bonds must be broken in order to melt or boil each of these: SiO2 KCl Cu CO C(diamond) BaSO4 NH3 NH4F C2H5OH N2 Fe HCl H2O Xe

Explain the difference in boiling points. CH3OCH3 -25°C CH3CH2OH 79°C HF 20°C HCl -85°C CH3CH2CH2CH2CH3 36°C CH3CH2CH3 -42°C

Which of these has the highest mp or bp? HCl, Ar, F2 H2O, NaCl, HF, C12H22O11 Cl2, Br2, I2 KO2 or SiO2

Classify as metallic, molecular,ionic or network covalent solid that a. is a nonconductor, but conducts when melted. b. dissolves in water to give a nonconducting solution. c. conducts electricity as a solid. d. melts below 100°C to give a nonconducting liquid.

Greatest Order Least T2 > T1 Evaporation Condensation

The equilibrium vapor pressure is the vapor pressure measured when a dynamic equilibrium exists between condensation and evaporation. It depends only on temperature. H2O (l) H2O (g) Rate of condensation evaporation = Dynamic Equilibrium 11.8

Before Evaporation At Equilibrium 11.8

Clausius-Clapeyron Equation Molar heat of vaporization (DHvap) is the energy required to vaporize 1 mole of a liquid. ln P = - DHvap RT + C Clausius-Clapeyron Equation P = (equilibrium) vapor pressure T = temperature (K) R = gas constant (8.314 J/K•mol) 11.8

The boiling point is the temperature at which the (equilibrium) vapor pressure of a liquid is equal to the external pressure. The normal boiling point is the temperature at which a liquid boils when the external pressure is 1 atm. 11.8

What are two differences between boiling and evaporation? A liquid boils at the temperature at which its vapor pressure equals the external pressure. high elevation - pressure cooker Boulder, CO 610 mm Hg is normal pressure – water boils at 94 °C Climate? Storms?

The critical temperature (Tc) is the temperature above which the gas cannot be made to liquefy, no matter how great the applied pressure. The critical pressure (Pc) is the minimum pressure that must be applied to bring about liquefaction at the critical temperature. ° 11.8

H2O (s) H2O (l) The melting point of a solid or the freezing point of a liquid is the temperature at which the solid and liquid phases coexist in equilibrium Melting Freezing 11.8

Molar heat of fusion (DHfus) is the energy required to melt 1 mole of a solid substance. 11.8

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Calculate the amount of heat that must be added to 2.50 moles of ice At -40°C to convert it to 2.50 moles of steam at 130 °C . Specific heats: ice 2.03 J/g °C steam 1.99 J/g °C , water 4.18 J/g °C

H2O (s) H2O (g) Molar heat of sublimation (DHsub) is the energy required to sublime 1 mole of a solid. Sublimation Deposition DHsub = DHfus + DHvap ( Hess’s Law) 11.8

A phase diagram summarizes the conditions at which a substance exists as a solid, liquid, or gas. Phase Diagram of Water 11.8

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Phase Diagrams for CO2 and H2O

Supercritical fluid I atm = 105 Pa Phase diagram for water showing different solid phases.

Use the following data to sketch a phase diagram for ethylene. bp at 1 atm -103.7 °C fp at 1 atm -169.16 °C critical pt. 9.9 °C and 50.5 atm triple pt. -169.17 °C and 0.0012 atm

Fig. 12.28

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