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CAS CH 109 (19)
Chapter 6

Chapter 6_Outline.docx

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Department
Chemistry
Course
CAS CH 109
Professor
Sean Elliott
Semester
Fall

Description
Savan Shah CH 109 Chapter 6 Outline Chapter 6: Liquids and Solids I. Intermolecular Forces -Phase  Form of matter that is uniform throughout in both chemical composition and physical state • Condensed Phases  Solids and liquids; When gas is cooled, condenses to liquid or solid • Ion-Ion: oTypical Energy = 250 kJ•mol -1 z1 2 oE =p 4πεr o1/r factor oIons only oWidely separated molecules come closer together  Energy initially falls  As distance becomes very small, energy increases  Repulsions become dominant  When no bond forms  Minimum is reached when molecules are farther apart than when they do form bonds • Ion-Dipole: oTypical energy = 15 kJ•mol -1 oAttachment of water molecules to solute particles  Hydration oDue to polar character of water molecule oHydration arises from interaction between ion and partial charges on polar water molecules  Ion-Dipole interaction 2 o1/r factor oIons and polar molecules oIon-Dipole < Ion-Ion  Dipole moment of polar molecule arises from only partial charges oPolar molecules need to be very close to ion before interaction is significant oAt large distances, attraction and repulsion cancel out interaction Savan Shah CH 109 Chapter 6 Outline oSize of ion and its charge control extent of hydration  Smaller cations are more extensively hydrated than large cations  Higher charge = Higher extent of hydration • Dipole-Dipole: -1 oTypical energy = 2 kJ•mol oMolecules lined up with opposite partial charges on neighboring molecules  Dipole-Dipole o1/r factor oWhen separation doubles, interaction falls to 1/8 initial strength  Based on 1/r,1/r2 factor oOccur between polar molecules oRapid falling off  Caused when distance between molecules increases (opposite partial charges on each molecule appear to merge and cancel) oLiquid interactions of molecules more powerful  Molecules are closer together oStrong IMFs = Higher Boiling Temperatures • London Dispersion Forces (Induced DP-Induced DP) oTypical Energy = 2 kJ•mol -1 oOccur between all types of molecules oInstantaneous Dipole Moment  Momentary separation of charge (Distorts electron cloud on neighboring molecule and gives rise to dipole moment in different direction) oStrength depends on polarizability  Highly polarizable molecules  Nuclear charges have little control over surrounding electrons (Atoms are large and distance between electrons is a lot, much shielding) o1/r factor oStrength increases with increasing polarizability  Large molecule with many electrons is more polarizable (More LDFs than smaller molecule) oEx: Noble Gases oIncrease as you go down groups (Halogen group) Savan Shah CH 109 Chapter 6 Outline oMore LDFs = Higher boiling point oShape of molecule also contributes to strength of intermolecular forces  2 rod-like shapes have greater LDFs than 2 sphere-like shapes (More contact points) oDipole-Induced Dipole -1  Typical Energy = 2 kJ•mol  Polar molecule interacts with nonpolar molecule (Ex: Oxygen dissolving in water)  Arises from ability of one molecule to induce dipole moment in the other  One molecule already must have permanent dipole (polar molecule) oLDFs and Dipole-Induced Dipole are known as Van Der Waals Forces • Hydrogen Bonding -1 oTypical Energy = 20 kJ•mol oHydrogen atom is bonded to small, strongly electronegative atom (N, O, or F)  Attracted to lone pair of electrons on another N, O, or F atom oDominates any other intermolecular forces that the molecule might have oDimers  Pairs of identical molecules (ex: Vapor of acetic acid) -Repulsions  Intermolecular repulsions arise from overlap of orbitals on neighboring molecules and requirements of Pauli exclusion principle II. Liquid Structure -Liquids contain highly disordered movement, and are intermediates between the gas and solid phases • Long-Range Order Atoms and molecules lie in orderly arrangement that is repeated over long distances (crystalline solids) oLiquids  Kinetic energy of molecules can overcome IMFs, molecules can move past one another, but still contain strong attractions for one another oShort-Range Order  The immediate vicinity of molecule in liquid is like that in the solid, but ordering does not extend very far past nearest neighbors • Viscosity  Resistance to flow (Higher viscosity of liquid, more sluggish flow) oIndicator of strength of intermolecular forces oAlso depends on ease with which molecules can take up new positions as fluid flows oDecreases
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