Outline
Intermolecular 12 Forces: Liquids, Solids, and Phase Changes 12.1 An overview of Physical States and Phase Changes Intramolecular Forces- bonding forces that exist in each molecule and influence chemical props Intermolecular Forces- nonbonding forces that exist btwn molecules and influence physical properties. A Kinetic-Molecular View of the Three States State depends on interplay of potential nrg of intermolecular forces. Different props- compressibility, shape an ability to flow. Gas has high nrg, liq med, solid lowest Types of Phase Changes Condensation- gas to liquid Vaporization- liquid to gas Freezing- liquid solidification Melting/Fusion- solid to liquid *Condensation and Freezing are exothermic s *Melting and Vaporization are endothermic s Heat of Vaporization H (vap) is the enthalpy per mole
More nrg is required to remove forces that connect molecules in fixed positions Sublimination- solid to gas Deposition- gas to a solid H (subl) 12.2 Quantitative Aspects of Phase Change Heat involved in Phase Changes: A Kinetic-molecular Approach Heating-Cooling Curve- shows the s that occur when heat is added or removed from a particular sample of matter at a constant rate. Five heat-releasing stages: Stage 1- Gaseous Water Cools Stage 2- Gaseous Water Condenses Stage 3- Liquid Water Cools Stage 4- Liquid Water Freezes Stage 5- Solid Water Cools
The Equilibrium Nature of Phase Changes - phase changes of many substances are irreversible
Liquid-Gas Equilibria Dynamic Equilibrium- the point where the forward and reverse processes are taking place at the same rate, so there is no net change in the amounts of reactants and products Vapor Pressure recorded at some specified temp The Effects of Temperature and Intermolecular Forces on VP The higher the temp, the higher the VP The weaker the intermolecular forces, the higher the VP ln P = (- H(vap)/ R) (1/T) + C ln P is the natural log of VP R is the universal gas constant 8.31 T is the absolute temperature C is a constant Clausius-Clapeyron Equation gives the nrg needed to vaporize 1 mol of molecules into the liquid state. ln (P2/P1) = (- Hvap/R) [(1/T2) (1/T1)] Vapor Pressure and the Boiling Point Boiling Point- is the temp at which the vapor pressure equals the external pressure and is dependant upon the applied pressure Solid-Liquid Equilibria Melting point is = to that of the freezing point, with a different flow in direction Solid-Gas Equilibria A sub sublimes instead of melting bc the combo of intermolecular forces and atmospheric pressure is not great enough to keep the particles near one another as they leave the solid state Phase Diagrams: Effects on Pressure and Temperature on Physical State Phase Diagram- combines the liq-gas, the solid-liq, and solid-gas curve 1. Regions of the Diagram- each regions corresponds to a different phase 2. Lines Between Regions- Rep phase-transition curves
3. Critical Point- where vapor cannot be condensed into a liq 4. The Triple Point- where pressure and temp of the 3 phases are at equilibrium 12.3 Types of Intermolecular Forces Bonding forces are strong bc they involve larger changes that are closer together while Intermolecular forces are weak bc they involve smaller changes and are farther apart. Van der Waals radius- the dist btwn the nuclei of two identical atoms unbonded atoms divided by two and is larger than the radius. covalent Types of forces: ion-dipole, dipole-dipole, hydrogen bonding, dipole-induced dipole, and dispersion forces. Ion-Dipole Forces ion and nearby polar molecule Dipole-Dipole Forces The positive pole of one molecule attracts the negative pole of another. Has higher boiling points and takes more nrg to disassociate. The Hydrogen Bond An h atom bonded to a small, highly EN atom with lone e- pairs. The Significance of Hydrogen Bonding Increase nrg needed for phase change initiation. Polarizability and Charge-Induced Dipole Forces Polarizability is the ease at which an e- cloud can be distorted. Pol inc down a group bc the e- cloud inc in size with atomic size, and the further the e-cloud from the nucleus allows for easier distortion Pol dec from left to right bc as Zeff shinks, the e- are held more closely. Cations are less pol than parent atoms, anions more pol bc they're bigger. Pol affects all intermolecular forces Dispersion (London) Forces Caused by momentary oscillations of e- charge in atoms, and , therefore are present btwn all particles. When e- clouds are close together, one instaneous dipole may influence another dipole of its neighbor. Pol depends on the # of ewhich correlates with molar mass 12.4 Properties of the Liquid State Surface Tension
Molecules at surface experience a net downward attraction and has the smallest possible surface. Surface tension- the nrg required to inc the surface area by a unit amt. The stronger forces btwn the particles in the liquid, the greater the surface tension. Capillarity Capillary action- the rising of liquid through a narrow space against the pull of gravity caused by competition btwn intermolecular forces within the liquid (cohesive) and the tube walls (adhesive). Difference in adhesive and cohesive strengths determines the concavity of the meniscus. Viscosity Viscosity is the resistance to flow, dec with heating, and dec with more spherical shapes. 12.5 The Uniqueness of Water Very polar, bent, and two lone pairs. Solvent Properties Solvent power results from its polarity and H-bonding ability. It dissolves ionic cmpds in ion-dipole forces Thermal Properties of Water High specific heat capacity. High heat of vaporization. Surface Properties of Water Remarkable thermal properties due to high surface tension and high capillarity. The Density of Solid and Liquid Water The solid state has a lower density. 12.6 The Solid State: Structure, Properties, and Bonding Structural Features of Solids Crystalline well defined shape with particles arranged orderly Amorphous poorly defined shapes and particles lack order Crystal lattice- points that form a regular pattern in a crystal and consists of all points with identical surroundings and those arrangements points define the types of lattice. Unit cell- the smallest portion of the crystal and creates a crystal if repeated in three directions The coordination number- neighbor of nearest surrounding neighbors 1. Simple cubic unit cell- the centers of eight identical particles define the corners of the cube
2. Body-centered cubic unit cell- identical particles lie at each corner and in the center of the cub; those corners do not touch. 3. Face-centered Cubic unit cell- identical particles lie at each corner and in the center of each face, not in the center of the cube. Packing Efficiency and the Creation of Unit Cells