Ch. 16: Ch. 16: Liquids and Solids Liquids and Solids

Intermolecular Forces Intermolecular Forces

Intra- vs. Inter-Intra- vs. Inter-

intramolecular forcesintramolecular forces inside moleculesinside molecules hold atoms together into moleculehold atoms together into molecule

intermolecular forcesintermolecular forces between moleculesbetween molecules get weaker as phase changes from S – L – get weaker as phase changes from S – L –

GG When a substance changes state, When a substance changes state,

molecule stays together but molecule stays together but intermolecular forces weakenintermolecular forces weaken

Dipole-Dipole AttractionDipole-Dipole Attraction

when molecules when molecules with dipole with dipole moments line up to moments line up to minimize repulsion minimize repulsion and maximize and maximize attractionattraction

very weak very weak compared to compared to covalent and ionic covalent and ionic bondsbonds

Hydrogen BondingHydrogen Bonding

happens between H and N, O, or Fhappens between H and N, O, or F very strong type of dipole-dipole very strong type of dipole-dipole

attractionattraction because bond is so polarbecause bond is so polar because atoms are so smallbecause atoms are so small

London Dispersion Forces London Dispersion Forces

in every molecular compoundin every molecular compound only important for nonpolar only important for nonpolar

molecules and noble gas atomsmolecules and noble gas atoms weak, short-livedweak, short-lived caused by formation caused by formation

of temporary of temporary

dipole moments dipole moments

PracticePractice which has highest boiling pt?which has highest boiling pt?

HF, HCl, or HBr?HF, HCl, or HBr? Identify the most important Identify the most important

intermolecular forces :intermolecular forces : BaSOBaSO44

HH22SS XeXe CC22HH66

PP44

HH22OO CsICsI

ionic

dipole-dipole

H-bonding

London Dispersion

Which has stronger IMF’s?Which has stronger IMF’s?

COCO22 or OCS or OCS COCO22: nonpolar so : nonpolar so

only LDonly LD OCS: polar so OCS: polar so

dipole-dipoledipole-dipole

PFPF33 or PF or PF55

PFPF33: polar so : polar so dipole-dipoledipole-dipole

PFPF55: nonpolar so : nonpolar so only LDonly LD

SFSF22 or SF or SF66

SFSF22: polar so : polar so dipole-dipoledipole-dipole

SFSF66: nonpolar so : nonpolar so only LDonly LD

SOSO33 or SO or SO22

SOSO33: nonpolar so : nonpolar so LD onlyLD only

SOSO22: polar so : polar so dipol-dipoledipol-dipole

Liquids and Solids Liquids and Solids

Properties of Properties of LiquidsLiquids

low compressibilitylow compressibility no rigidityno rigidity high density compared to high density compared to

gasesgases beads up as droplets beads up as droplets

molecules on surface are molecules on surface are subject to attractions from subject to attractions from side and belowside and below

surface tensionsurface tension resistance to an increase resistance to an increase

in surface areain surface area greater tension means greater tension means

stronger IMF’sstronger IMF’s

Properties of LiquidsProperties of Liquids capillary actioncapillary action

spontaneous rising of a liquid up spontaneous rising of a liquid up a tubea tube

from cohesive forces (IMF’s) and from cohesive forces (IMF’s) and adhesive forces (between liquid adhesive forces (between liquid and container)and container)

viscosityviscosity measure of a liquid’s resistance measure of a liquid’s resistance

to flowto flow strong IMF’s strong IMF’s highly viscous highly viscous large, complex molecules large, complex molecules highly highly

viscousviscous

Practice QuizPractice Quiz