W20-Chem-260-L16.pdf - Chem 260 Chemistry 260 Interactions...

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Chem 260Lecture 161Chemistry 260Lecture 16February 14, 2020Today in Chemistry 260• non-covalent interactions (intermolecular forces)• ionic “bonds”• electrostatic interactions & distance• intermolecular forces & distance• hydrogen bondsNext in Chemistry 260• reading Chang 2.1-4.• gases?Exam #1: Monday, Feb. 17, 6-8 PMCheck Canvas announcement for room assignmentsAll alternates have been notifiedBring – 1 note sheet (8.5 by 11 both sides), pencils, erasers, calculatorInteractions in Chemistry1. Atoms contain positive nuclei and negative electrons+Ze-erV r( )=14πε0q1q2r=14πε0+Ze()e()r=14πε0Ze2rThe ±Coulomb²potential describes interactions between charged particlesThe MOST IMPORTANTpotential energy function in chemistrye= 1.6022³10-19Coulombse0= 8.85418782 ³10-12m-3kg-1s4A2Charles-Augustin de CoulombConsider the points labeled above. For which points isthe force between the nuclei repulsive?A.AB.BC.CD.DE.C and DExample: hydrogenmoleculeABCDConcept QuestionTranslocation of DNA through a membrane in alpha-hemolysin.Non-bonding interactions are electrostatic, a combination ofchargescharge distributions“distortability” of charge dist.J. Mathé, A. Aksimentiev, D. R. Nelson, K. Schulten, and A. MellerPNAS USA, 102:12377-12382, 2005.Intermolecular InteractionsIonic Interactions:+-r1/r long range interaction proportional to the product of chargesnot directionalV(r)=qAqB4πεorABElectrostatic InteractionsV(r)=|qAqB|4πεorIf qAand qBare opposite chargeV(r)=|qAqB|4πεorIf qAand qBare same charge
Chem 260Lecture 162Interaction Between IonsCoulombic attractionbetween oppositely charged ions.V(r)=qAqB4πεorAB=ZAe()ZBe()4πεorABFor an ionic solid =LATTICE ENERGYHighest lattice energy: smallerions and larger chargeIonic solid -- infinite array of cations and ions stacked together to yield the lowest-energy arrangement.Interaction Between IonsThe lattice energy of a salt therefore gives a rough indication of the solubility of the salt in water because it reflects the energy needed to separate the positive and negative ions in a salt.Lattice EnergyEach ion experiences attractions andrepulsionsPotential energy (lattice energy) is the sum of all of thesedFor a one-dimensional array of +Z and –Z ions, the potential felt by one ion:+-+-ddddV1=Z2e24πεod112+1314+!

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