suggested reading (from the 7 th ed): 1) page 380, i suggest you read the first paragraph in section...

Suggested Reading (from the 7th ed):

1) Page 380, I suggest you read the first paragraph in section 8.8 if not the entire section.

2) Review Example 8.12 on pg 384 to make sense of why NH3 is more polar than NF3, which at first seems odd.

3) Read the bottom of pg 558 beginning with, “When a polar…” to “…dipole-dipole attraction.”

4) Read three paragraphs on pg 562, starting with “There is an unusually strong…” to “…(Figure 12.7).”

5) On pg 565-567, read the two sections: “Dipole/Induced Dipole Forces” and “London Dispersion Forces: Induced Dipole/Induced Dipole”.

HH

water dipole

••

••

O-

+

Recall molecular polarity…?

12.1Know the level of intermolecularforces for each state of matter,s, l, g.

Which has the most and which has none?

A: The opposite ends of their dipoles: opposites attract…..and like polarities “stick” to like polarities.

Q: What makes molecules “stick” together in the liquid (and solid) state?

Opposites attract…..and like polarities “stick” to like polarities.

Different Levels of Molecular Polarity

A

DE

B C

H

Know the level and types of intermolecular attractions for molecules in the solid & liquid states

A: Intermolecular forces (attractions): The sticking power between molecules that keep molecules in a solid or a liquid state

Electrostatic attractions occur when an electrically positive region is attracted to an electrically negative region. So called dipoles exist in each molecule.

Intermolecular attractions arise because of weak electrostatic attractions between molecules.

Asymmetrical distribution of electrically positive region(s) and electrically negative region(s), i.e. dipole(s), are inherent in polar molecules, such as HF & H2O.

H-FO

H Hδ+

δ+

δ-

δ-

δ+

Symmetrical distribution of electrically positive region(s) and electrically negative region(s), i.e. no dipole, are inherent in nonpolar molecules, such as BF3 & CH4.

BF F

F

C

H

H

H

H

A: Molecules induce dipoles on other molecules

Q: If dipoles are needed for electrostatic attractions between molecules to keep them together in the liquid & solid states then how do nonpolar molecules (those without a dipole) “stick” together to form liquids & solids?

12.2 Know the following intermolecular attractions that exist in pure liquids and solids and in dissolved molecules and ions.

Induced Dipole – Induced DipoleInduced Dipole – Induced DipoleInduced Dipole – Induced DipoleInduced Dipole – Induced Dipole

Formation of dipoles in Formation of dipoles in two nonpolartwo nonpolar molecules: molecules:

Induced dipole-Induced dipoleInduced dipole-Induced dipole

Intermolecular Attraction Polar ? Example Strength

Induced Dipole- Induced Dipole No-No N2 to N2 Weakest

Dipole-Induced Dipole Yes-No H2O to O2

Dipole-Dipole Yes-Yes Moderate

Regular HCl to HCl

H-Bonding (limited to F, O, N)

H2O to H2O H2O to NH3

Dipole-Ion Yes-** Strongest

Formation of dipoles in a Formation of dipoles in a nonpolar and a polarnonpolar and a polar molecule: molecule:

Induced dipole-dipoleInduced dipole-dipole

Dipole – Induced DipoleDipole – Induced DipoleDipole – Induced DipoleDipole – Induced Dipole

Intermolecular Attraction Polar ? Example Strength

Induced Dipole- Induced Dipole No-No N2 to N2 Weakest

Dipole-Induced Dipole Yes-No H2O to O2

Dipole-Dipole Yes-Yes Moderate

Regular HCl to HCl

H-Bonding (limited to F, O, N)

H2O to H2O H2O to NH3

Dipole-Ion Yes-** Strongest

Diploe – DipoleDiploe – DipoleRegular Regular

Diploe – DipoleDiploe – DipoleRegular Regular

Intermolecular Attraction Polar ? Example Strength

Induced Dipole- Induced Dipole No-No N2 to N2 Weakest

Dipole-Induced Dipole Yes-No H2O to O2

Dipole-Dipole Yes-Yes Moderate

Regular HCl to HCl

H-Bonding (limited to F, O, N)

H2O to H2O H2O to NH3

Dipole-Ion Yes-** Strongest

Diploe – DipoleDiploe – DipoleH-bonding H-bonding

At least one of the molecules must have a HH atom COVALENTLY COVALENTLY bonded to a NN or an OO or a FF atom ANDAND the other molecule must have a NN or an OO or a FF atom.

Intermolecular Attraction Polar ? Example Strength

Induced Dipole- Induced Dipole No-No N2 to N2 Weakest

Dipole-Induced Dipole Yes-No H2O to O2

Dipole-Dipole Yes-Yes Moderate

Regular HCl to HCl

H-Bonding (limited to F, O, N)

H2O to H2O H2O to NH3

Dipole-Ion Yes-** Strongest

H-Bonding Between Two H-Bonding Between Two Methanol MoleculesMethanol Molecules

H-Bonding Between Two H-Bonding Between Two Methanol MoleculesMethanol Molecules

H-bondH-bondH-bondH-bond

--++

--

H-Bonding Between Methanol and WaterH-Bonding Between Methanol and Water

H-bondH-bondH-bondH-bond--

++

--

H-Bonding Between H-Bonding Between Ammonia and WaterAmmonia and WaterH-Bonding Between H-Bonding Between Ammonia and WaterAmmonia and Water

H-bondH-bondH-bondH-bond

--

++ --

H-Bonding

Base-Pairing through H-Base-Pairing through H-BondsBonds

Base-Pairing through H-Base-Pairing through H-BondsBonds

Hydrogen bonding and base pairing in DNA.Hydrogen bonding and base pairing in DNA.

Ion - DiploeIon - Diploe

Intermolecular Attraction Polar ? Example Strength

Induced Dipole- Induced Dipole No-No N2 to N2 Weakest

Dipole-Induced Dipole Yes-No H2O to O2

Dipole-Dipole Yes-Yes Moderate

Regular HCl to HCl

H-Bonding (limited to F, O, N)

H2O to H2O H2O to NH3

Dipole-Ion Yes-** Strongest

Apply the concept of intermolecular forces to predict solubility between substances: Like polarities dissolve Like polarities.

Unlike polarities DO NOT dissolve Unlike polarities.

CH3CH2CH2CH2CH2CH2CH2CH2CH2-

c

Boiling LiquidsBoiling LiquidsA liquid boils when its vapor pressure

equals atmospheric pressure.A liquid boils when its vapor pressure

equals atmospheric pressure.

How intermolecular attractions relate to boiling points

CHCl3

CH3CH2OHH2OCH3COOH

120

461860

62

78100118

Chloroform

EthanolWaterAcetic acid

NameMolecularFormula

MolecularWeight(amu)

BoilingPoint(°C)

CH3CH2CH2CH2CH2CH3 86 69Hexane

Boiling points of covalent compounds depend primarily on two factors:

(1) the nature and strength of intermolecular attractions

(2) molecular size and shape.

Increasing Boiling

Point

The vapor pressure of a given molecule at a given The vapor pressure of a given molecule at a given

temperature depends on intermolecular temperature depends on intermolecular

attractions. attractions.

C2H5H5C2 HH5C2 HH

wateralcoholether

Increasing strength of IM attractions

extensiveH-bondsH-bonds

dipole-dipole

OOO

Increasing vapor pressure

bp = 35oC bp = 78oC bp = 100oC

CHCH44

CC22HH66

CC33HH88

CC44HH1010

Boiling Point trends in a Homologous Series

CH3CH3

CH4

CH3CH2CH3

CH3CH2CH2CH3