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”.

Recall molecular polarity…?

12.1 Know the level of intermolecular forces for each state of matter, s, l, g. Which has the most and which has none?

Q: What makes molecules “stick” together in the liquid (and solid) state? A: The opposite ends of their dipoles: opposites attract…..and like polarities “stick” to like polarities.

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

Different Levels of Molecular Polarity B A H D E

A: Intermolecular forces (attractions): The sticking power between molecules that keep molecules in a solid or a liquid state Know the level and types of intermolecular attractions for molecules in the solid & liquid states

Intermolecular attractions arise because of weak electrostatic attractions between molecules. Electrostatic attractions occur when an electrically positive region is attracted to an electrically negative region. So called dipoles exist in each molecule.

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. δ- O H δ+ δ- H-F 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. B F C 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? A: Molecules induce dipoles on other molecules

Induced Dipole – Induced Dipole Formation of dipoles in two nonpolar molecules: Induced dipole-Induced dipole

Dipole – Induced Dipole Formation of dipoles in a nonpolar and a polar molecule: Induced dipole-dipole

Diploe – Dipole Regular

Diploe – Dipole H-bonding At least one of the molecules must have a H atom COVALENTLY bonded to a N or an O or a F atom AND the other molecule must have a N or an O or a F atom.

H-Bonding Between Two Methanol Molecules - + - H-bond

H-Bonding Between Methanol and Water - H-bond + -

H-Bonding Between Ammonia and Water - + - H-bond

H-Bonding

Base-Pairing through H-Bonds Hydrogen bonding and base pairing in DNA.

Ion - Diploe

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

A liquid boils when its vapor pressure equals atmospheric pressure. Boiling Liquids A liquid boils when its vapor pressure equals atmospheric pressure.

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 temperature depends on intermolecular attractions. Increasing vapor pressure C 2 H 5 water alcohol ether Increasing strength of IM attractions extensive H-bonds dipole- dipole O bp = 35oC bp = 78oC bp = 100oC

Boiling Point trends in a Homologous Series CH4 C2H6 C3H8 C4H10 CH4 CH3CH3 CH3CH2CH3 CH3CH2CH2CH3