Chapter 11 Liquids and Solids and Intermolecular Forces Georgia Gwinnett College Chem 1212K Fall 2013 B Shepler Chapter 11 1 Phases of Matter SOLIDS Have rigid shape fixed volume External shape can reflect the atomic and molecular arrangement Reasonably well understood LIQUIDS Have no fixed shape and but do have a fixed volume Not well understood GASES Expand to fill their container No fixed shape or volume Good theoretical understanding Chapter 11 3 Intermolecular versus bonding forces Bonding Forces Chemical bonds covalent ionic metallic Strong Directional Short Range relative Intermolecular Forces Weaker than chemical bonds usually much weaker Less directional than covalent bonds more directional than ionic bonds Longer range than covalent bonds but at shorter range than ionic bonds Condensed Phases Solids and Liquids Intermolecular forces mutual attractions hold the molecules closer together than gases Sometimes call covalent bonds intramolecular forces Chapter 11 4 Dipole Dipole Interaction A dipole dipole interaction occurs when both molecules have a dipole moment Consider the molecule acetone CH3COCH3 The partial positive end of one molecule is attracted to the partial negative end of another molecule This is a dipole dipole interaction 5 Hydrogen Bonding Hydrogen bonds are a special type of dipoledipole interaction It occurs between an H bonded to an O N or F on one molecule and an O N or F on another molecule Stronger than typical dipole dipole interactions The boiling points of the covalent hydrides of elements in Groups 4A 5A 6A and 7A Importance of Hydrogen Bonding Chapter 11 7 Example Illustrate the dipole dipole interaction that occur between multiple molecules of dimethyl ether CH 3OCH3 Can molecules of dimethyl ether hydrogen bond to one another Can a molecule of dimethyl ether hydrogen bond to a molecule of water Chapter 11 8 Dispersion Forces Dispersion Forces London Dispersion Forces Result of fluctuations in the electron distribution within molecules or atoms At one instant the electrons may be unevenly distributed Chapter 11 9 The instantaneous dipole moment on one atom molecule induces an instantaneous dipole moment on another atom molecule The instantaneous dipole moments then attract each other Chapter 11 10 Dispersion Forces London dispersion forces The weakest intermolecular force Exist between all atoms molecules even if they also possess stronger intermolecular forces Polarizability The ability of the electron cloud to be distorted More polarizable means greater dispersion forces Tends to increase with atom molecular size larger electron clouds Cations are significantly less polarizable than their parent atom The shape of a molecule can effect the dispersion forces Chapter 11 11 Example Which atom molecule in each pair have higher boiling points 1 Ne or Xe 2 Chapter 11 12 Ion Dipole Interactions Ion dipole interactions Occur between an ion such as Na and any polar compound Chapter 11 13 Induced Dipole Interactions ion induced dipole interactions or dipole induced dipole interactions The electron cloud of a molecule can be distorted by a nearby electric field Results in a temporary induced dipole moment Argon Atom Argon Atom Chapter 11 14 Review Chapter 11 15 Ionic Bonds No molecules in ionic compounds Ionic bonds can be considered both intermolecular and intramolecular Strongest of intermolecular forces 400 to 4000 kJ mole Explains why ionic solids tend to have HIGH melting points temperatures Chapter 11 16 Determining Most Important Intermolecular Force between 2 or more molecules Draw the Lewis Structures Determine Bond Polarities Use Geometry Shape to determine molecule polarity identify possibility of H bonding etc Chapter 11 17 Examples Determine the primary intermolecular forces that are present in a sample of each of the following BaBr 2 CH3COOH NH3 H2S and SiH4 and CH2ClBr Chapter 11 18 Like Dissolves Like Chapter 11 19 Liquids and Intermolecular Forces Surface Tension Chapter 11 20 Liquids and Intermolecular Forces Viscosity Chapter 11 21 Phase Changes GAS SOLID LIQUID Chapter 11 22 Vaporization Vaporization and Condensation Factors that effect the rate of vaporization Temperature Surface Area Intermolecular Forces Chapter 11 23 Vapor Pressure and Dynamic Equilibrium Dynamic Equilibrium When two opposite processes react at the same rate Not net gain or loss of material Vapor pressure Pressure of gas in dynamic equilibrium with its liquid Chapter 11 24 Vapor Pressure and Intermolecular Forces Which of the following compounds has the greater vapor pressure at 25 C Water Dimethyl Ether CH3OCH3 Ethanol CH3CH2OH Chapter 11 25 Temperature Dependence of Vapor Pressure and Boiling Point Boiling Point temperature at which the vapor pressure equals the external pressure atmospheric Molecules in the interior of the liquid can break free from the intermolecular forces Normal Boiling Point Temperature at which the vapor pressure equals 1 atm 760 torr Chapter 11 26 Phase Diagrams We have seen in this chapter that the phase of a substance depends on both its temperature AND its pressure A phase diagram is a map of the phase of a substance as a function of temperature and pressure Chapter 11 27 A Typical Phase Diagram Chapter 11 28 Unusual Phases of Matter Triple Point A unique temperature and pressure at which all three phases of matter can be in equilibrium with one another t butanol triple point 25 C and 44 mmHg Supercritical Fluid Critical point Temperature and pressure above which the phase boundary between liquids and gasses cease to exist Supercritical fluid the phase of matter that exists at T and P above the critical point Has many properties of gasses but can dissolve things like a liquid Many industrial applications Supercritical SF6 Chapter 11 29 Chapter 11 Problem Determine the phases of matter for the following points on the phase diagram of CO2 following conditions a 20 0 C 72 9 atm b 56 7 C 5 1 atm c 10 0 C 1 0 atm d 78 5 C 1 0 atm e 50 0 C 80 0 atm