Concepts and Trends
What is the weakest type of intermolecular force found in all molecules?
London-Dispersion Forces
Stronger intermolecular forces generally result in a higher _________________.
Boiling point
What is the main IMF in CO2?
London Dispersion
Why do stronger intermolecular forces generally result in a higher boiling point?
Stronger IMFs require more energy to separate molecules, so the boiling point increases.
Why does water have a higher boiling point than H2S?
Water forms hydrogen bonds (stronger bonds); H2S cannot
What IMF's does H2O have?
Mainly dipole-dipole = water molecule is polar
Hydrogen bonding with other molecules
London Dispersion Forces = temporary attractions from movement of electrons
Rank the intermolecular forces in order from weakest to strongest.
Dispersion Forces -> Dipole-Dipole Forces -> Hydrogen Bonding -> Ion-Dipole Forces -> Ionic Bonding
Why does a nonpolar substance (eg. oil) not dissolve in water?
Because non-polar molecules cannot form IMFs with polar molecules ("like dissolves like")
Which IMF is present in HF that explains its high boiling point?
Hydrogen Bonding
Why are hydrogen bonds stronger than regular dipole-dipole forces?
Hydrogen bonds involve very electronegative atoms (N, O, F) creating stronger partial charges.
How does molecular size affect the boiling point in a non-polar molecule?
Larger molecules = more electrons = stronger dispersion forces = higher boiling point
Rank the intermolecular forces in these molecules from weakest to strongest: CO2, HBr, H2O
(weakest) CO2, HBr, H2O (strongest)
Predict which IMF dominates in each I2, HF, and CH3Cl, and explain how the molecular structure determines this.
I2 = London Dispersion
HF = Hydrogen Bonding
CH3Cl = Dipole-Dipole
Which has a higher boiling point? CH4 or C3H8? Why?
C3H8 because it has a larger mass = stronger London Dispersion = higher boiling point.
Identify all the IMFs in CH3OH and label each one with the bond to which it belongs.
Between C and H's and C and O -> Dipole-Dipole
Hydrogen with nearby O from another molecule -> hydrogen bonding
London dispersion -> all over = from temporary fluctuations in electron distribution.