Presentation on theme: "Suggested Reading (from the 7 th 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."— Presentation transcript:
Suggested Reading (from the 7 th 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 NH 3 is more polar than NF 3, 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 , 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?
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 D E 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 & H 2 O. H-F O HH δ+δ+ δ+δ+ δ-δ- 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 BF 3 & CH 4. B F 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?
Induced Dipole – Induced Dipole Formation of dipoles in two nonpolar molecules: Induced dipole-Induced dipole
Formation of dipoles in a nonpolar and a polar molecule: Induced dipole-dipole Dipole – Induced Dipole
Diploe – Dipole Regular Regular
H-bonding H At least one of the molecules must have a H atom COVALENTLY NOFAND COVALENTLY bonded to a N or an O or a F atom AND NOF the other molecule must have a N or an O or a F atom.
H-Bonding Between Two Methanol Molecules H-bondH-bond - + -
H-Bonding Between Methanol and Water H-bondH-bond - + -
H-Bonding Between Ammonia and Water H-bondH-bond - + -
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.
CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 -
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. C 2 H 5 H 5 C 2 H H 5 C 2 H H wateralcoholether Increasing strength of IM attractions extensive H-bonds dipole- dipole O O O Increasing vapor pressure bp = 35 o C bp = 78 o C bp = 100 o C
CH 4 C2H6C2H6C2H6C2H6 C3H8C3H8C3H8C3H8 C 4 H 10 Boiling Point trends in a Homologous Series CH 3 CH 4 CH 3 CH 2 CH 3 CH 3 CH 2 CH 2 CH 3