Outline for Today Monday, Nov. 26 Chapter 11: Intermolecular Forces - - PowerPoint PPT Presentation

Outline for Today

Monday, Nov. 26

• Chapter 11: Intermolecular Forces and Liquids
• Intermolecular Foces
• Comparing States of Matter
• Properties of Liquids
• Phase Changes

1

Exam 3 Reminders

• When: Wednesday at 5pm
• Where: First floor of Keyes
• What: Cumulative with a focus on chapters 6 through 9
• Review Session Tonight 7-9pm Keyes 105

Chapter 6: Electronic Structure of Atoms

• There are 4 equations related to the wave behavior of light

and matter, know when and how to use them!

• Know the rules for the quantum numbers and how they

relate to orbital shapes and number of nodes.

• Be able to write electron configurations for all elements.
• Don’t forget: there are 4 exceptions to the electronic

configuration patterns (Cr, Cu, Ag, Au)

Chapter 7: Periodic Trends

• There are 4 periodic trends we discussed.
• ZEff, sizes of atoms and ions, ionization energy, and

electron affinity.

• You should know the definitions, trends, and reasons why

each trend occurs.

• You should be able to rationalize exceptions based on

electron configurations.

Chapter 8: Chemical Bonding

• Identify Ionic Bonding and Lattice Energy
• Lewis Structures
• Formal Charge
• Bond Polarity and Trends in Electronegativity
• Resonance structures and exceptions to the octet

rule

• Calculations using Bond Enthalpy

Chapter 9: Molecular Geometry and Bonding Theories

• Three dimensional molecular shapes (Tables 9.1 through

9.4)

• Orbital Hybridization and Multiple bonds
• Molecular Polarity (REALLY IMPORTANT for Chapter 11!)
• Molecular orbital theory for 1st and 2nd row diatomic

(figure 9.43)

• Bond Order and Paramagnetic/Diamagnetic

A Brief Review of Polarity and Dipole Moments

• Draw a Lewis Structure of CF2I2.
• Is it Polar or Nonpolar?

Chapter 11: Intermolecular Forces and Condensed Phases

(Liquids and Solids)

The waxy molecules coating the lotus leaf are different than the water! They are Hydrophobic! Why? Intermolecular Forces! (The waxy lotus leaves lack hydrogen bonding!) Why does the water droplet bead up on the lotus leaf? Why doesn’t it spread out?

Intermolecular Forces are the Forces of INTERACTING Molecules

Cl2 Br2 I2

Gas Liquid Solid Strongly Interacting. Strong Intermolecular Forces Weakly Interacting. Weak Intermolecular Forces

Intermolecular Forces

• Intermolecular Forces= The attractive forces between

molecules

Intermolecular Forces

• London Dispersion: Attraction between

momentary or instantaneous dipoles in molecules.

• Dipole-Dipole: Attraction between partial

charges due to permanent dipoles

• Hydrogen-Bonding: Attraction between

partial charges on H-F , H-O, or H-N bonds.

• Ion-Dipole: Attraction between ions and

partial charges of dipoles Generally Weaker Generally Stronger

Intermolecular Forces

• London Dispersion: Attraction between

momentary or instantaneous dipoles in molecules.

• Dipole-Dipole: Attraction between partial

charges due to permanent dipoles

• Hydrogen-Bonding: Attraction between

partial charges on H-F , H-O, or H-N bonds.

• Ion-Dipole: Attraction between ions and

partial charges of dipoles

All Molecules Needs H attached to O, N, or F Polar Molecules Needs an Ion

van der Waals forces

Which Molecules?

London Dispersion

Strength of London Dispersion Forces depends on Polarizability

• Polarizability: How easy it is to alter the electron density
• f a molecule (how sloshy the electrons is)
• Polarizability tends to increase with the number of

electrons (roughly molecular weight).

• Example: Order the following molecules from most

polarizable to least:

• F2, I2, Cl2
• SnH4, SiH4, CH4

Stronger the Intermolecular Force, the Higher the Boiling Point Temperature!

• Example: Sort the following by increasing Boiling Point

Temperature

• H2Te, H2S, H2Se

London-Dispersion Depends on Shape

Same Molecular Weight, Different Shapes Different Boiling Points

Dipole-Dipole

• Dipole-Dipole: Attraction between partial charges due to

permanent dipoles.

• Example: Is there a dipole on CH3CN?
• How do the dipoles interact?

Dipole-Dipole Interactions in Solids

Dipole Dipole Interactions in Liquids

The larger the dipole, the stronger the dipole-dipole interactions!

O O N

Increasing Polarity Increasing Dipole-Dipole Interactions Increasing Boiling Point

Hydrogen-Bonding is a special type of dipole interaction

• Hydrogen-Bonding: Attraction between partial charges
• n H-F

, H-O, or H-N bonds.

• H-F

, H-N, and H-O are especially polar bonds!

• They interact strongly with small electronegative ions or

atoms (like F , O, or N of another molecule).

• That interaction is called hydrogen bonding.

NOT A Hydrogen Bond

C H H H H

Yes, there are hydrogens bonded to stuff, but there is no intermolecular hydrogen bonding interaction. There is no hydrogen bond.

C H H H H

Hydrogen Bonding Is Critical for Understanding the Properties of Water!

Predict the relative strengths of the dipole-dipole interactions

• Order the following by increasing boiling point (based on

strength of the intermolecular interactions)

a) Butane c) 2-Methylpropane O d) Isopropyl alcohol b) Propyl alcohol O

Intermolecular Forces with Charged Particles

• Ion-Dipole Forces: Attraction (or Repulsion) between an

ion and the partial charge on the end of a molecule

Try this chart with: Ammonia, Methane, Acetic Acid, Hydrochloric Acid