Intermolecular Forces

Intermolecular Forces

Phase of Matter	Properties
gas	assumes volume and shape of container
gas	compressible
gas	flows readily
gas	diffusion through it is rapid
liquid	assumes shape of container but keeps its own volume
liquid	virtually incompressible
liquid	flows readily
liquid	diffusion through it is slow
solid	keeps its own shape and volume
solid	virtually incompressible
solid	does not flow
solid	diffusion through it is extremely slow
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Intermolecular Forces	Properties
Electrostatic Forces	less than about 15% the strength of covalent and ionic bonds
Electrostatic Forces	includes London dispersion forces, dipole-dipole forces, H-bonds, and ion-dipole forces
Van Der Waals Forces	includes London dispersion forces, dipole-dipole forces, and H-bonds
Van Der Waals Forces	forces between neutral molecules
London Dispersion Forces	occur between all molecules
London Dispersion Forces	stronger for larger mass molecules and more polarizable molecules
London Dispersion Forces	gives >80% of HCl's intermolecular interactions
dipole-dipole forces	for molecules of the same size and mass, these forces are stronger for the molecule with the more polar bonds
dipole-dipole forces	for molecules of the same polarity, these forces are stronger for the molecule with the smaller volume
H-bonds	these are unusually strong dipole-dipole forces
H-bonds	occur between a polar bond and an unshared electron pair (a lone pair) on a nearby electronegative ion or atom
H-bonds	usually occur in molecules containing N-H, O-H, or H-F bonds
H-bonds	4 to 25 kJ/mol, much weaker than chemical bonds, but much stronger than dipole-dipole and London dispersion forces
ion-dipole forces	occur in solutions where ionic compounds are dissolved in polar liquids
ion-dipole forces	occur between charged particles and the ends of polar molecules
ion-dipole forces	stronger than dipole-dipole forces
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Intermolecular Forces	Systems where they are important
London Dispersion Forces	Ar(l), I2(s)
dipole-dipole forces	H2S, CH3Cl
H-bonds	H2O, NH3, HF
ion-dipole forces	NaCl or KBr dissolved in water
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When ranking the strength of intermolecular forces in several pure substances each made up of a single molecule (like C₂H₆ vs. C₃H₈ vs. C₄H₁₀), the following are true:

Fill in the blanks	Answers
If the molecules all have similar masses and shapes, ____.	the London Dispersion Forces are all similar
If the molecules all have similar masses and shapes, ____.	dipole-dipole forces decide the ranking
If the molecules all have similar masses and shapes, ____.	the intermolecular forces rise as the bond polarity rises
If the molecules all have very different molecular weights, ____.	the London Dispersion Forces are all different
If the molecules all have very different molecular weights, ____.	the London Dispersion Forces decide the ranking
If the molecules all have very different molecular weights, ____.	the intermolecular forces rise as the molecular weight rises
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If Intermolecular Forces are ____	This property is high
strong	heat of vaporization
strong	specific heat
strong	melting point
strong	boiling point
strong	viscosity
strong	surface tension
strong	critical temperature
strong	critical pressure
weak	vapor pressure
weak	volatility
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Fill in the blanks	Answers
Viscosity rises as the temperature ____.	falls
Vapor Pressure rises as the temperature ____.	rises
The critical temperature is the ____.	highest temperature for a liquid. Above this temperature, the liquid and gas phases aren't distinct
The critical pressure is the ____.	vapor pressure at the critical temperature
Cohesive forces attract molecules of one substance to ____.	other molecules of the same substance
Adhesive forces attract molecules of one substance to ____.	molecules of a different substance
A concave meniscus occurs when ___.	adhesive forces dominate over cohesive ones
A concave meniscus occurs when ___.	the level of liquid in a capillary tube is higher near the capillary tube walls than it is near the center of the capillary tube
A concave meniscus occurs when ___.	water is in a capillary tube
A convex meniscus occurs when ___.	cohesive forces dominate over adhesive ones
A convex meniscus occurs when ___.	the level of liquid in a capillary tube is lower near the capillary tube walls than it is near the center of the capillary tube
A convex meniscus occurs when ___.	mercury is in a capillary tube
Ionic bonds are important in ____.	NaCl and NH4NO3
Metallic bonds are stronger than ____.	H-bonds
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Crystalline Solid	Intermolecular Forces	Properties	Examples
Molecular	LDF, dpl-dpl, H-bonds	soft, low to moderately high melting point, poor thermal and electrical conductivity	Ar, ice, methane (CH4), sucrose, dry ice (CO2)
Covalent Network	covalent bonds	very hard, high melting point, poor thermal and electrical conductivity	diamond (C), graphite (C), silicon (Si), quartz (SiO2)
Ionic	electrostatic	hard, brittle, high melting point, poor thermal and electrical conductivity	salts, NaCl, Ca(NO3)2, CaF2
Metallic	Metallic bonds	soft to very hard, malleable, ductile, low to very high melting point, high thermal and electrical conductivity	Cu, Fe, Al, Pt, Ag, Brass
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Unit Cell	Number of Atoms Per Unit Cell	% of volume occupied by atoms	Coordination Number (Number of Equidistant Nearest Neighbors)
primitive cubic	1	52%	6
BCC (body-centered cubic)	2	68%	8
FCC (face-centered cubic) CCP (cubic-closest-packed) ABCA	4	74%	12
HCP (hexagonal-closest-packed) ABAB	4	74%	12
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