What are intermolecular forces (IMFs)?
Forces of attraction between neighboring molecules that influence physical properties like boiling point.
Name the three main types of intermolecular attractions.
London dispersion forces (LDFs), dipole-dipole interactions, and hydrogen bonds.
Describe London dispersion forces.
Weak, temporary forces present in all molecules (polar or nonpolar), resulting from instantaneous, temporary dipoles caused by random electron movement.
Describe dipole-dipole interactions.
Attractions between the permanent positive and negative ends (poles) of adjacent polar molecules.
Describe hydrogen bonds.
A special, strong type of dipole-dipole interaction between a hydrogen atom (bonded to O, N, or F) and a lone pair of electrons on a neighboring O, N, or F atom.
Rank the three main IMFs from weakest to strongest.
Hydrogen bonds > Dipole-dipole interactions > London dispersion forces.
How do you determine if a molecule is polar or nonpolar?
A molecule is polar if it has a permanent dipole due to unequal sharing of electrons (a large difference in electronegativity) and an asymmetrical shape (e.g., water, H₂O). It is nonpolar if electron distribution is symmetrical (e.g., methane, CH₄).
What type of IMF(s) does a nonpolar molecule like methane (CH4) have?
Only London dispersion forces.
What type of IMF(s) does a polar molecule like hydrogen chloride (HCl) have?
Dipole-dipole interactions and London dispersion forces (all molecules have LDFs).
What type of IMF(s) does a molecule like water (H2O) have?
All three: London dispersion forces, dipole-dipole interactions, and hydrogen bonds (due to O-H bonds).
Is water (H20) a polar or nonpolar molecule?
Polar, due to the bent shape and high electronegativity of oxygen creating partial charges.
Will methanol (CH3OH) be soluble in water? Why?
Yes, because both are polar and can form hydrogen bonds with each other (“like dissolves like”).
Will oil (a large nonpolar hydrocarbon) be soluble in water? Why?
No. Oil is nonpolar and water is polar; they cannot form strong attractions (like hydrogen bonds) with each other.
