Intermolecular Attractions & the Properties of Liquids & Solids CHAPTER 12 Chemistry: The Molecular Nature of Matter, 6 th edition By Jesperson, Brady, & Hyslop REVIEW

Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E 2 Strength of Intermolecular Forces CHAPTER 12 Concept Review London Dispersion Forces Dipole-Dipole Forces Hydrogen Bonds (a type of Dipole-Dipole Force) Ion-Dipole or Ion-Induced Dipole Forces Weakest Strongest

Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E 3 Strength of Intermolecular Forces CHAPTER 12 Concept Review London Dispersion Forces: minimized surface area London Dispersion Forces: maximized surface area Dipole-Dipole Forces: small overall dipole moment Dipole-Dipole Forces: large overall dipole moment Hydrogen Bonds: with 1 H-bond per molecule Hydrogen Bonds: with multiple H-bonds per molecule Ion-Dipole or Ion-Induced Dipole Forces Weakest Strongest

Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E 4 Strength of Intermolecular Forces CHAPTER 12 Concept Review

Property of s, l, gIncreasesDecreasesExample Boiling Point Melting Point Compressibility Diffusion Retention of V & Shape Surface Tension Wetting Viscosity

Property of s, l, gIncreasesDecreasesExample Boiling Point increasing total intermolecular forces decreasing total intermolecular forces Water has a high boiling point because it has H-bonding, dipole, and dispersion forces. It is close to heptane (C7H16), a heavier molecule that only experiences dispersion forces. Melting Point increasing total intermolecular forces decreasing total intermolecular forces The melting point of ionic solids is extremely high compared to water which experiences all other intermolecular forces, but not ion-dipole forces. (NaCl is 1074 K and water is 273 K) Compressibility increasing distance between collisions with other particles decreasing distance between collisions with other particles Gases are very compressible because the particles have higher kinetic energies, and great distances between particles. Diffusion with increasing kinetic energy & increased distance between collisions with deceasing kinetic energy & decreased distance between collisions Diffusion is much slower in a solid or in a liquid and much faster in a gas. Retention of V & Shape Increasing intermolecular forces and decreasing T & P Decreasing intermolecular forces, and increasing kinetic energy of particles or T & P Gases will fill the volume and shape of the container that holds them, while solids will retain their own shape and volume regardless of the container. Surface Tension with increasing intermolecular forces with decreasing intermolecular forces The molecules on the surface have less neighbors (and therefore less stabilizing intermolecular forces) and so have a higher potential energy, which the material will try to reduce with its shape (sphere): water beading. Wetting when there are fewer intermolecular attractions to overcome in order to interact with the surface When the intermolecular forces in the liquid are stronger then the intermolecular forces with the surface Water beads on a greasy surface rather then wetting because the dipole forces and hydrogen bonds are so much stronger then the dispersion forces that water experiences with the surface. If the surface is clean it can experience dipole forces and hydrogen bonds with the oxygen in SiO2. Viscosity increasing intermolecular forces and decreasing temperature decreasing intermolecular forces and decreasing temperature Not just a property of liquids, also gases and solids. Amorphous solids change shape over time because of their viscosity.

7 Phase Changes = changes of physical state with temperature ( α to KE) SOLID LIQUIDGAS fusion freezing evaporation condensation deposition sublimation endothermic exothermic System absorbs energy from surrounds in the form of heat o Requires the addition of heat System releases energy into surrounds in the form of heat or light o Requires heat to be decreased

TEMPERATURE HEAT ADDED HEATING CURVE solid liquid gas s l l g fusion ΔH fus evaporation or vaporization ΔH vap endothermic

9 Equilibrium & Phase Diagrams T 1 = 78°C P 1 = 330 atm To increase T 2 = 100°C The system must respond by increasing P 2 = 760 to restore equilibrium: o T is higher o Volume of liquid is lower o P of vapor higher

Le Chatelier’s Principle Liquid + Heat  Vapor If you increase either the liquid or the heat the reaction is driven to the right to re- establish equilibrium. If you increase vapor the reaction will be driven to the left to re-establish equilibrium. Liquid + Heat  Vapor

11 3-D Simple Cubic Lattice Portion of lattice— open view Unit Cell Space filling model

Other Cubic Lattices 12 Face Centered Cubic Body Centered Cubic

SiteCounts asShared by X unit cells Body11 Face1/22 Edge1/44 Corner1/88 Counting Atoms in Unit Cells

14 Interpreting Diffraction Data Bragg Equation nλ=2d sinθ –n = integer (1, 2, …) – = wavelength of X rays –d = interplane spacing in crystal –  = angle of incidence and angle of reflectance of X rays to various crystal planes

15 Example: Using Diffraction Data X-ray diffraction measurements reveal that copper crystallizes with a face-centered cubic lattice in which the unit cell length is 362 pm. What is the radius of a copper atom expressed in picometers? This is basically a geometry problem.

16 Ex. Using Diffraction Data (cont.) diagonal = 4  r Cu = 512 pm r Cu = 128 pm Pythagorean theorem: a 2 + b 2 = c 2 Where a = b = 362 pm sides and c = diagonal 2a 2 = c 2 and