intermolecular forces. intra- vs. inter- intra-: inward –ex. intradermal, intravenous inter-:...

Intermolecular ForcesIntermolecular Forces

Intra- vs. Inter-Intra- vs. Inter- IntraIntra-:-: inward inward

– Ex. Intradermal, IntravenousEx. Intradermal, Intravenous Inter-Inter-:: between or among between or among

– Ex. Interstate, InternationalEx. Interstate, International IntraIntramolecular forces act molecular forces act withinwithin a a

molecule.molecule.– Ionic, covalent, and metallic bondingIonic, covalent, and metallic bonding

InterIntermolecular forces act molecular forces act betweenbetween molecules.molecules.– London dispersion, dipole-dipole interactions, London dispersion, dipole-dipole interactions,

ion-dipole interactions, and Hydrogen bondingion-dipole interactions, and Hydrogen bonding

Intramolecular vs. Intermolecular Intramolecular vs. Intermolecular Forces - SimilaritiesForces - Similarities

Attractive forcesAttractive forces Force due to electron sharing Force due to electron sharing

(charge)(charge) Affect spatial arrangements of atoms Affect spatial arrangements of atoms

and molecules, respectivelyand molecules, respectively

Intramolecular vs. Intermolecular Intramolecular vs. Intermolecular Forces - DifferencesForces - Differences

Intramolecular Intramolecular ForcesForces

Intermolecular Intermolecular ForcesForces

StrongStrong WeakWeak

Act within moleculesAct within molecules Act between moleculesAct between molecules

Persist for life of Persist for life of moleculemolecule

More brief in life of More brief in life of moleculemolecule

Not strongly effected by Not strongly effected by physical changesphysical changes

Strongly effected by Strongly effected by physical changesphysical changes

Stabilize individual Stabilize individual moleculesmolecules

Responsible for bulk Responsible for bulk properties of matterproperties of matter

Lava Lamp ExperimentLava Lamp Experiment1.1. Each pair of students should write their names on the top of 1 sheet Each pair of students should write their names on the top of 1 sheet

of paper.of paper.2.2. One student should obtain a 250 mL beaker and fill halfway with One student should obtain a 250 mL beaker and fill halfway with

water.water.3.3. A second student should add about 1 cm of oil to top (between ¼ A second student should add about 1 cm of oil to top (between ¼

and ½ inch or about the width of pinky finger).and ½ inch or about the width of pinky finger).4.4. On your piece of paper, draw and describe the beaker and label it On your piece of paper, draw and describe the beaker and label it

as “Drawing 1”.as “Drawing 1”.5.5. When Drawing 1 is complete, raise your hand for addition of 1 drop When Drawing 1 is complete, raise your hand for addition of 1 drop

of food coloring.of food coloring.6.6. Draw the beaker and its contents immediately after the addition of Draw the beaker and its contents immediately after the addition of

food coloring. Label this “Drawing 2”.food coloring. Label this “Drawing 2”.7.7. Wait 1-2 minutes and draw the beaker again. This is “Drawing 3”.Wait 1-2 minutes and draw the beaker again. This is “Drawing 3”.8.8. When Drawings 2 and 3 are complete, raise your hand for addition When Drawings 2 and 3 are complete, raise your hand for addition

of sugar.of sugar.9.9. Draw and describe what happens right after the sugar is added as Draw and describe what happens right after the sugar is added as

“Drawing 4”.“Drawing 4”.10.10. Draw and describe what happens about one minute after the sugar Draw and describe what happens about one minute after the sugar

is added as “Drawing 5”.is added as “Drawing 5”.

Lava Lamp ExperimentLava Lamp Experiment

1.1. What materials will mix together?What materials will mix together?2.2. What happened to food coloring in oil? How What happened to food coloring in oil? How

would you describe the color, shape, size, and would you describe the color, shape, size, and movement of the food coloring?movement of the food coloring?

3.3. What happened to food coloring in water? How What happened to food coloring in water? How would you describe the color, shape, size, and would you describe the color, shape, size, and movement of the food coloring?movement of the food coloring?

4.4. What do you think the phrase “like dissolves What do you think the phrase “like dissolves like” means?like” means?

5.5. How would you apply “like dissolves like” to the How would you apply “like dissolves like” to the materials used in the beaker?materials used in the beaker?

Intermolecular ForcesIntermolecular Forces

London dispersion forcesLondon dispersion forces Dipole-dipole forcesDipole-dipole forces Hydrogen bondingHydrogen bonding Ion-dipole forcesIon-dipole forces

Name Name of of

forceforce

Rank of Rank of strengthstrength

Ion Ion involved?involved?

Polar or Polar or nonpolar nonpolar

molecules?molecules?

Is H Is H involved?involved?

ExampleExample

Why don’t oil and water mix?Why don’t oil and water mix?

London dispersion forcesLondon dispersion forces Weakest Weakest

intermolecular forceintermolecular force Only attractive force Only attractive force

between non-polar between non-polar moleculesmolecules

Created from Created from temporary fluctuations temporary fluctuations in electron density in electron density around atomsaround atoms

The larger the The larger the molecule, the greater molecule, the greater the dispersion force.the dispersion force.

https://www.chem.unsw.edu.au/coursenotes/CHEM1/nonunipass/hainesIMF/dispersion.html

London dispersion forcesLondon dispersion forces

Why don’t oil and water mix?Why don’t oil and water mix?


Which materials exhibit London Which materials exhibit London dispersion forces?dispersion forces?

What observations can be explained What observations can be explained by London dispersion forces?by London dispersion forces?

Name of Name of forceforce


Ion involved?Ion involved? Polar or Polar or nonpolar nonpolar



ExampleExample

London London dispersion dispersion forcesforces

44 NoNo Both (strongest Both (strongest for nonpolar)for nonpolar)

NoNo Oil and waterOil and water

DipoleDipole

In polar molecules electrons are not In polar molecules electrons are not equally shared between atoms.equally shared between atoms.

In areas of the electron cloud where In areas of the electron cloud where electrons are more likely to be found, a electrons are more likely to be found, a “dipole” is formed. This end of the “dipole” is formed. This end of the molecular has a partial negative charge. molecular has a partial negative charge. The opposing side of the molecule will The opposing side of the molecule will have a partial positive charge.have a partial positive charge.

These molecules are “polar”.These molecules are “polar”.

DipoleDipole

H

Cl

H H

O

Example: HCl Example: H2O

δ+ δ+δ+

δ -δ -δ -

Images modified from: http://employees.csbsju.edu/hjakubowski/classes/ch123/ch123ch2mcmfay5th.htm

Dipole-Dipole ForcesDipole-Dipole Forces

Attractive force Attractive force between neutral, between neutral, polar molecules polar molecules (molecules that (molecules that possess a dipole).possess a dipole).

The larger the The larger the dipole, the greater dipole, the greater the force.the force.

AnimationAnimation

Image modified from: http://www.chem.ufl.edu/~itl/2041_u01/lectures/lec_g.html


What materials exhibit dipole-dipole What materials exhibit dipole-dipole interactions?interactions?

What observations can be explained What observations can be explained by dipole-dipole interactions?by dipole-dipole interactions?






ExampleExample




Dipole-Dipole-dipole dipole forcesforces

33 NoNo PolarPolar NoNo Alcohol in Alcohol in waterwater

Why does salt dissolve?Why does salt dissolve?

Ion-Dipole ForcesIon-Dipole Forces

Interaction between Interaction between charged molecule charged molecule (ion) and polar (ion) and polar molecule (dipole).molecule (dipole).

Strength depends on Strength depends on charge and size of ion charge and size of ion and magnitude and and magnitude and size of dipolesize of dipole– Cations interact more Cations interact more

strongly with dipoles strongly with dipoles than anions.than anions.

Image from: http://www.chem.purdue.edu/gchelp/liquids/iondip.html

Why does salt dissolve? Why does salt dissolve? NaCl in Water

How would heating affect solubility? Stirring?


Were there any ion-dipole forces in Were there any ion-dipole forces in the lava lamp experiment?the lava lamp experiment?

Can any observations be explained Can any observations be explained by ion-dipole forces?by ion-dipole forces?






ExampleExample






Ion-dipole Ion-dipole forcesforces

11 YesYes PolarPolar NoNo Salt in waterSalt in water

Hydrogen BondingHydrogen Bonding

Permanent Permanent dipole-dipole dipole-dipole interactioninteraction

Only occurs in Only occurs in molecules molecules containing H-F, containing H-F, H-N, or H-O H-N, or H-O bondsbonds

A H B

Where A and B are F, N, or O

Hydrogen Bonding of WaterHydrogen Bonding of Water

Hydrogen Bonding of Water

SnowflakesSnowflakes

Hydrogen Bonding & Boiling PointHydrogen Bonding & Boiling Point

Image from: http://faculty.ycp.edu/~peterman/chm136/chm136s07ex1a.htm


Were there any hydrogen bonds in Were there any hydrogen bonds in the lava lamp experiment?the lava lamp experiment?

Can any observations be explained Can any observations be explained by hydrogen bonding?by hydrogen bonding?






ExampleExample






Ion-dipole Ion-dipole forcesforces

11 YesYes PolarPolar NoNo Salt in waterSalt in water

Hydrogen Hydrogen bondingbonding

22 NoNo PolarPolar YesYes WaterWater

““Like dissolves like”Like dissolves like”

To be soluble a compound must To be soluble a compound must interact with the solute by:interact with the solute by:– Dipole-dipole forcesDipole-dipole forces– Ion-dipole forcesIon-dipole forces– London dispersion forcesLondon dispersion forces

Polar solutes dissolve in polar Polar solutes dissolve in polar solutionssolutions

Non-polar solutes dissolve in non-Non-polar solutes dissolve in non-polar solutionspolar solutions

SummarySummary

Image from: http://www.chem.ufl.edu/~itl/2041_u01/lectures/lec_g.html

intermolecular forces. intra- vs. inter- intra-: inward –ex. intradermal, intravenous inter-:...

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dipoledipole interactions

polar molecules molecules

materials exhibit dipole

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polar molecules electrons

nonpolar molecules

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