! Final Exam Study Guide Lectures: 1 - 40Lectures 1 and 2 (1/5 and 1/7) • there exists intermolecular forces between gases, liquids, and solids o ionic forces (ion – ion): Coloumb’s Law states that there is an attraction proportional to the product of the distance between the centers of the two atoms o intermolecular (no charges): § a) Dipole – Dipole (dip-dip): between polar covalent molecules, or molecules that have a permanent dipole moment § b) Hydrogen Bonding (special type of dip-dip): molecules contain one of the highly electronegative atoms Fluorine, Oxygen, or Nitrogen (FON) § c) London Dispersion Forces (LDFs): attractions between atoms or uncharged, non-polar molecules such as CH4 • the farther you move down a period, the bigger the electron clouds get à increased polarizability (the squishability of the electron cloud) à easier for LDFs to act because dipole moments come about easier when electrons are easier to snatch away • heavier molecules (increased molecular weight) = more LDFs• always present as a force o intramolecular forces are generally stronger; these forces include ionic, covalent, and metallic forces (to be covered later) Lecture 2 (1/7) and associated readings: • PROPERTIES • Viscosity: resistance of a liquid to flow o depends on the attractive forces between molecules o for related compounds (such as hydrocarbons), viscosity increases with molecular weight o for any given substance, viscosity decreases with increasing temperature• Surface tension: imbalance of IMFs at the surface leads the molecules there to experience a net inward/downward pull; this reduces the surface area and makes them pack closely together • Capillary action: the rise of liquid up very narrow tubes o binding of similar molecules is called cohesive forces • PHASE CHANGES o every phase change also has an energy change/transfer associated with it o melting is also called fusion: the increased freedom of motion of the particles requires energy, measured by the heat of fusion ΔHfus § gas to liquid = condensation § liquid to gas = vaporization § liquid to solid = freezing § solid to liquid = melting/fusion§ solid to gas = sublimation § gas to solid = deposition • heat of vaporization ΔHvap is the energy required to turn liquid to gas • ΔHvap is usually greater than ΔHfus for a substance because the energy that is needed to completely mobilize all participles is greater • HEATING CURVES !!!!!CHEM!1312H!!1stEdition!Edited with the trial version of Foxit Advanced PDF EditorTo remove this notice, visit:www.foxitsoftware.com/shopping! !o enthalpy changes can be calculated from heating curves o • heat in J (used to calculate the slope-y parts of the heating curve, so AàB and CàD) q = (mass in grams)(specific heat)( ΔT ) • heat energy (used to calculate flat parts of curve, so BàC and DàE) q = (mass in grams)( either ΔHfus or ΔHvap) • CRITICAL TEMPERATURE AND PRESSURE o critical temperature: the highest temperature at which a distinct liquid phase can exist o critical pressure: the pressure required to bring about liquefaction at the critical temperature • VAPOR PRESSURE o the pressure exerted by a vapor o dynamic equilibrium: condition in which two opposing processes occur simultaneously at equal rates o liquids that evaporate readily are volatile Lecture 3 (1/9) • Liquid crystals: “hybrids” between solids and liquids so that there is still some movement within the crystal among particles, but there is also enough structure so as to remain a solid o a) normal liquid o b) nematic liquid crystal (refer to Lecture 3 for illustrations) o c) smectic A liquid crystal (refer to Lecture 3 for illustrations) o d) smectic C liquid crystal (refer to Lecture 3 for illustrations) o molecules align along the long axis to maximize IMFs o pitch: distance required for the top layer of molecules in a cholesteric structure to be replicated after a certain number of rotations (refer to Lecture 3 for illustrations) § if the pitch is larger, you’re diffracting longer wavelengths of light and vice versa: red lights = longer pitches, blue lights = shorter pitches § as you change the temperature, you also change the pitch distance • heat the liquid, pitch gets smaller, turns more blue • cool the liquid, pitch gets longer, turns more red § to make a liquid crystal: • you want long, rod-like rigid molecules :rf3+r(l*o''aa^'ffq pd,4#r} un.rta-^d.,mblS +h#qt? 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