[http://cwx.prenhall.com/bookbind/pubbooks/mcmurry2/medialib/fig10.gif]

[http://ds9.ssl.berkeley.edu/LWS_GEMS/2/images_2/pom535.jpg]

InterIntermolecular Forcesmolecular Forces

• Forces of attraction between two or more molecules.

• Can help determine how a chemical changes between a solid, liquid, or gas.

[http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH11/FG11_01.JPG]

Intermolecular ForcesIntermolecular Forces

• Hydrogen Bonding

• Occurs in molecules where F, N, or O are bonded to an H atom.

• Strongest of the “forces”

[http://www.saburchill.com/IBbiology/chapters01/images/11010328.jpg]

Highest boiling points

[http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH11/FG11_21.JPG]

Intermolecular ForcesIntermolecular Forces

• Dipole – Dipole Force

• Force that attracts polar molecules to one another.

• Only occurs in polar molecules

• Moderate “force”

[http://darkwing.uoregon.edu/~ch111/images/electroneg.gi]f

Electronegativity Values

Remember – Elements that are more electronegative “pull” the electrons in a

bond closer

H

H

OO OC

Polar vs. Nonpolar

[http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter10/Text_Images/FG10_04.JPG]

[http://cwx.prenhall.com/bookbind/pubbooks/mcmurry2/chapter10/medialib/TB10_002.JPG]

Intermolecular ForcesIntermolecular Forces

• Dispersion Forces• Since electrons are

always moving they could temporarily concentrate on one side of a molecule.

• These occur in all molecules.

• Weakest of the “forces”[http://www.chem.unsw.edu.au/coursenotes/CHEM1/nonunipass/HainesIMF/images/dispersion.jpg]

[http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter10/Text_Images/FG10_TB03.JPG]

Heavier mass = Stronger Dispersion Force

[http://cwx.prenhall.com/bookbind/pubbooks/mcmurry2/chapter10/medialib/TB10_005.JPG]

Comparison of the Forces

Intermolecular ForcesIntermolecular Forces

• Example:

• Which intermolecular forces are present in NH3 molecules?

Intermolecular ForcesIntermolecular Forces

• Dispersion Forces

• Dipole-Dipole Forces (it is polar!)

• Hydrogen Bonding (N-H bonds!)

[http://www.wackyscienceguy.com/khemistry/fall/covalent/quiz/images2/polaritynh3.jpg]

Intermolecular ForcesIntermolecular Forces

• Example:

• Which intermolecular forces are present in CH4 molecules?

Intermolecular ForcesIntermolecular Forces

• Dispersion Forces only!

[http://www.wackyscienceguy.com/khemistry/fall/covalent/quiz/images2/polaritynh3.jpg]

Intermolecular ForcesIntermolecular Forces

• Example:

• List the following from lowest melting point to highest melting point:

• CO2 (g), O2 (g), N2(g)

Intermolecular ForcesIntermolecular Forces

• All only have Dispersion Forces so…

• N2 (g) : 28.0 g/mol (lowest)

• O2 (g) : 32.0 g/mol

• CO2 (g) : 44.0 g/mol (highest)