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