topic: intermolecular forces part 2: dipole- dipole and hydrogen bonding do now: list the 4...

TOPIC: Intermolecular Forces Part 2: Dipole- Dipole and Hydrogen Bonding Do Now: List the 4 categories of Nonpolar Molecules – all of these have DISPERSION FORCES Noble Gas –group 18: He, Ne, Ar, Kr, Xe, Rn 7 diatomic elements H 2 , N 2 , O 2 , Cl 2 , F 2 , I 2 , Br 2 Pure Hydrocarbons – molecules with only C and H General formula C x H y : examples = CH 4 , C 2 H 6 , C 3 H 8 these 3 small symmetrical molecule CO 2 , CF 4 , CCl 4

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TOPIC: Intermolecular ForcesPart 2: Dipole- Dipole and Hydrogen Bonding

Do Now: List the 4 categories of Nonpolar Molecules – all of these have DISPERSION FORCES Noble Gas –group 18:

He, Ne, Ar, Kr, Xe, Rn

7 diatomic elements

H2, N2, O2, Cl2, F2, I2, Br2

Pure Hydrocarbons – molecules with only C and H

General formula CxHy : examples = CH4, C2H6, C3H8

these 3 small symmetrical molecule

CO2, CF4, CCl4

Page 2: TOPIC: Intermolecular Forces Part 2: Dipole- Dipole and Hydrogen Bonding Do Now: List the 4 categories of Nonpolar Molecules – all of these have DISPERSION

All molecules have Dispersion forces (the regents calls these Van der Waals)

2 other types of forces (IMF): 1. Dipole-Dipole forces2. Hydrogen bonds

-if one of these are present, they are more important.

Page 3: TOPIC: Intermolecular Forces Part 2: Dipole- Dipole and Hydrogen Bonding Do Now: List the 4 categories of Nonpolar Molecules – all of these have DISPERSION

2. Dipole-dipole forces: • Stronger then dispersion forces• occur between polar (asymmetrical)

molecules (they have a partial charge at each pole – one is typically much larger than the other)

• Click here for animation (slide 3 of 13)

http://www.wisc-online.com/Objects/ViewObject.aspx?ID=GCH6804

Page 4: TOPIC: Intermolecular Forces Part 2: Dipole- Dipole and Hydrogen Bonding Do Now: List the 4 categories of Nonpolar Molecules – all of these have DISPERSION

Dipole-dipole Forces & Polar Molecules

Polar Molecule shows permanent separation of charge; has poles: one end partially (-) & one end partially (+);Asymmetrical

http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH11/FG11_19.JPG

Page 5: TOPIC: Intermolecular Forces Part 2: Dipole- Dipole and Hydrogen Bonding Do Now: List the 4 categories of Nonpolar Molecules – all of these have DISPERSION

Page 6: TOPIC: Intermolecular Forces Part 2: Dipole- Dipole and Hydrogen Bonding Do Now: List the 4 categories of Nonpolar Molecules – all of these have DISPERSION

3. Hydrogen bonds:

• strongest IMF • occur between molecules that have an :

H-F H-O or H-N bonds ONLY

Strongest Intermolecular Force

Hydrogen Bonding

Dipole-Dipole

Dispersion

Hydrogen Bonding

H-O N-H

Occurs between molecules with H-F, H-O, or H-N bonds

http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter10/Text_Images/FG10_06-02UN.JPG

Hydrogen Bonding

Hydrogen bonding is extreme case of dipole-dipole bondingF, O, and N are all small and electronegative

strong electrons attraction H has only 1 electron, so if being pulled away H

proton is almost “naked” H end is always positive & F, O, or N end is always negative

Page 9: TOPIC: Intermolecular Forces Part 2: Dipole- Dipole and Hydrogen Bonding Do Now: List the 4 categories of Nonpolar Molecules – all of these have DISPERSION

Strength of Hydrogen BondingFluorine most electronegative element, so

H-F bonds are most polar and exhibit strongest hydrogen bonding, so strongest IMF

H-F is stronger than H-O which is stronger than H-N

(H-bonding…sound like FON to me!!!)

Page 10: TOPIC: Intermolecular Forces Part 2: Dipole- Dipole and Hydrogen Bonding Do Now: List the 4 categories of Nonpolar Molecules – all of these have DISPERSION

H-Bonding = strongest IMFmuch harder to “pull” molecules apart

Page 11: TOPIC: Intermolecular Forces Part 2: Dipole- Dipole and Hydrogen Bonding Do Now: List the 4 categories of Nonpolar Molecules – all of these have DISPERSION

Dispersion Forces= weakest IMFmuch easier to “pull” molecules apart

C H

Page 12: TOPIC: Intermolecular Forces Part 2: Dipole- Dipole and Hydrogen Bonding Do Now: List the 4 categories of Nonpolar Molecules – all of these have DISPERSION

Hydrogen bonding: • strongest IMF• influences physical props a great deal

H-F > H-O > H-N

IMF vs Physical PropertiesIf IMF then:

Boiling point Melting point Heat of Fusion Heat of Vaporization

while: Evaporation Rate

Change from solid to liquid w/o changing temp

Change from liquid to gas w/o changing temp

Rate at which conc. will go from liquid to gas

Page 13: TOPIC: Intermolecular Forces Part 2: Dipole- Dipole and Hydrogen Bonding Do Now: List the 4 categories of Nonpolar Molecules – all of these have DISPERSION

Why do some substances exist as gases, some as liquids, and some as solids at room temp?

#1 reason = IMF

Page 14: TOPIC: Intermolecular Forces Part 2: Dipole- Dipole and Hydrogen Bonding Do Now: List the 4 categories of Nonpolar Molecules – all of these have DISPERSION

If IMF are strong, substance will be solid or liquid at room tempParticles want to clump together

If IMF are weak, substance will be gas at

room tempParticles free to spread

apart

Page 15: TOPIC: Intermolecular Forces Part 2: Dipole- Dipole and Hydrogen Bonding Do Now: List the 4 categories of Nonpolar Molecules – all of these have DISPERSION

Why do some substances exist as gases, some as liquids, and some as solids at room temp?

#1 reason = IMF

#2 reason = temperature (avg. KE)

Page 16: TOPIC: Intermolecular Forces Part 2: Dipole- Dipole and Hydrogen Bonding Do Now: List the 4 categories of Nonpolar Molecules – all of these have DISPERSION

Temp = average KEIf we change T we change KEIncrease KE will help “pull” molecules

apart (overcome IMF)

Page 17: TOPIC: Intermolecular Forces Part 2: Dipole- Dipole and Hydrogen Bonding Do Now: List the 4 categories of Nonpolar Molecules – all of these have DISPERSION

Indicate type of IMF for each molecule:

NH3

ArN2

HClHFNeO2

HBrCH3NH2

• Hydrogen bonding• Dispersion forces• Dispersion forces• Dipole-dipole forces• Hydrogen bonding• Dispersion• Dispersion• Dipole-dipole• Hydrogen bonding

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