Attractive Forces Between Attractive Forces Between MoleculesMolecules

Which phase has particles more strongly Which phase has particles more strongly attracted?attracted?Solid , Liquid, Gas?Solid , Liquid, Gas?

Intermolecular Forces of AttractionIntermolecular Forces of Attraction

Forces of attraction Forces of attraction betweenbetween molecules. molecules.

Called “Called “Van der Waals ForcesVan der Waals Forces””They arise from weak “electrostatic attractions”They arise from weak “electrostatic attractions”

between particles.between particles.

Shows electrostatic attractions between opposite charged areas on molecules

Forces Between Polar MoleculesForces Between Polar Molecules

Dipole-Dipole AttractionsDipole-Dipole Attractions::Occurs between polar moleculesOccurs between polar moleculesPolar Molecule = “Dipole”Polar Molecule = “Dipole”

asymmetrical molecule with polar bondsasymmetrical molecule with polar bonds

Forces Between Polar MoleculesForces Between Polar Molecules

Hydrogen BondingHydrogen BondingDipole-Dipole Attraction but strongerDipole-Dipole Attraction but stronger

Occurs between molecules that have hydrogen Occurs between molecules that have hydrogen atoms bonded to very small, highly atoms bonded to very small, highly electronegative atoms like electronegative atoms like F, O or NF, O or N

Creates a very polar bond and an “extra polar” Creates a very polar bond and an “extra polar” molecule.molecule.

Results in Results in unusually high MP/BP tempsunusually high MP/BP temps..

Remember:Remember:Hydrogen Bonding is Hydrogen Bonding is ““FONFON”!!”!!

Hydrogen bonds are responsible for:Hydrogen bonds are responsible for: Ice Floating on WaterIce Floating on Water

Ice is ordered with an open structure to optimize Ice is ordered with an open structure to optimize H-bonding.H-bonding.

Therefore, ice is less dense than water.Therefore, ice is less dense than water.

Also it is responsible for water’sAlso it is responsible for water’sSurface tensionSurface tensionHow it beadsHow it beads

Forces Between Nonpolar MoleculesForces Between Nonpolar Molecules

Dispersion ForceDispersion Force (“weak force”) (“weak force”)Only attractive forces between Only attractive forces between nonpolarnonpolar

molecules and noble gas atoms.molecules and noble gas atoms.

WeakestWeakest of all intermolecular forces. of all intermolecular forces.

Instantaneous or “momentary” dipoles are formed Instantaneous or “momentary” dipoles are formed as electrons move around the atoms.as electrons move around the atoms.

Also called an “induced dipole” force.Also called an “induced dipole” force.

For nonpolar gases to become liquids:For nonpolar gases to become liquids:Gas particles are so far apart, weak dispersion Gas particles are so far apart, weak dispersion

forces cannot be felt.forces cannot be felt.

Molecules must be close and moving slowly so Molecules must be close and moving slowly so that the momentary dipoles can be createdthat the momentary dipoles can be created

High pressure/low temp. conditionsHigh pressure/low temp. conditions

Dispersion Forces have different strengthsDispersion Forces have different strengths..

The more The more total electronstotal electrons in a molecule, the in a molecule, the greater the force can get.greater the force can get.

Ex: Ex: ClCl22 has 34 electrons (it’s a gas) has 34 electrons (it’s a gas)

BrBr22 has 70 electrons (it’s a liquid) has 70 electrons (it’s a liquid)

II22 has 106 electrons (it’s a solid) has 106 electrons (it’s a solid)

Why Do Ionics Dissolve in Water?Why Do Ionics Dissolve in Water?

Molecule-Ion AttractionsMolecule-Ion Attractions::Attraction between polar solvent molecules Attraction between polar solvent molecules

and ions in an ionic crystal. and ions in an ionic crystal. Allows polar solvent (like water) to “pull” the Allows polar solvent (like water) to “pull” the

ions into solution, creating “hydrated” ions.ions into solution, creating “hydrated” ions.

Remember which side of water is negative!

 http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/thermochem/solutionSalt.html

What Effects do these Forces Have?What Effects do these Forces Have?

Melting and Boiling Point Temperature:Melting and Boiling Point Temperature:Stronger forces make it harder to separate Stronger forces make it harder to separate

molecules and undergo a phase change.molecules and undergo a phase change.

H-Bonding = highest MP/BPH-Bonding = highest MP/BPDispersion Forces = lowest MP/BPDispersion Forces = lowest MP/BP

Solubility:Solubility: solutes must form solutes must form

attractions to solvent to dissolve in it.attractions to solvent to dissolve in it.

Polar solvents attract polar solutesPolar solvents attract polar solutesNonpolar solutes only dissolve in nonpolar Nonpolar solutes only dissolve in nonpolar

solvents.solvents.Polar solvents can attract ions Polar solvents can attract ions

Viscosity : Viscosity : a measure of resistance

of a fluid to flow.

Stronger IMF = more viscosity

Since there are cohesive forces between the molecules of liquid, like intermolecular forces, these forces create an "internal friction" which reduces the rate of flow of that fluid, so when a substance has greater IMF, these frictional forces are stronger. Therefore, it has more resistance toward moving.

http://www.youtube.com/watch?v=f6spBkVeQ4whttp://www.youtube.com/watch?v=f6spBkVeQ4w

Vapor Pressure:Vapor Pressure:Pressure exerted by collisions of vapor Pressure exerted by collisions of vapor

particles above a liquidparticles above a liquid

The weaker the attractions The weaker the attractions

between molecules in a liquid, between molecules in a liquid,

the easier to become a gas.the easier to become a gas.

Therefore:Therefore:Nonpolars with weaker attractions have higher Nonpolars with weaker attractions have higher

VP than polarsVP than polars

Vapor PressureVapor Pressure

Measured in a closed system at a specific Measured in a closed system at a specific temperature.temperature.

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/vaporv3.swf

Vapor Pressure Vapor Pressure

If the temperature of a liquid increases, If the temperature of a liquid increases, what happens to VP?what happens to VP?

http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/propOfSoln/vp3.html

Vapor PressureVapor PressureBoiling Point:Boiling Point: occurs when VP equals the atmospheric occurs when VP equals the atmospheric

pressure pushing down on the liquid.pressure pushing down on the liquid.

Normal Boiling Point:Normal Boiling Point:The temp. a liquid boils at standard pressureThe temp. a liquid boils at standard pressure

1 atm1 atm101.3 KPa101.3 KPa760 mmHg (torr)760 mmHg (torr)

For water it is 100For water it is 100°°C.C.

Can you boil water at different Can you boil water at different Temperatures? Temperatures?

Yup! Yup!

It depends more on the amount of air It depends more on the amount of air pressure pushing down on the liquid.pressure pushing down on the liquid.

http://www.youtube.com/watch?v=8lyqFkFsH28&safe=active

Using Reference Table HUsing Reference Table H

Significant FiguresSignificant Figures

Click for Powerpoint:Click for Powerpoint:http://www.slideshare.net/crespiryan/http://www.slideshare.net/crespiryan/

significant-figures-550789significant-figures-550789

Sig Figs Practice:Sig Figs Practice:http://www.sciencegeek.net/Chemistry/http://www.sciencegeek.net/Chemistry/

taters/Unit0Sigfigs.htmtaters/Unit0Sigfigs.htm

Accuracy vs. PrecisionAccuracy vs. Precision

https://www.youtube.com/watch?https://www.youtube.com/watch?v=8Cl5CeiT7hUv=8Cl5CeiT7hU