Intermolecular Forces Quiz

Intermolecular Attractive Forces (IMAFs)

• IMAFs are forces between molecules.
• They increase in strength in the following order; London Dispersion Forces (LDFs), Dipole-Dipole (DD), Hydrogen Bonding (HB), Ion-Dipole (ID).
• LDFs arise from temporary dipoles formed from electron movement.
• Polarizability is the ease of distortion of an electron cloud.
• Higher polarizability correlates with stronger LDFs. Larger molecules and higher molecular weight often have stronger LDFs.
• DD arises between polar molecules that have a permanent dipole moment; the positive end of one molecule is attracted to the negative end of another.
• HB occurs when hydrogen is bonded to highly electronegative elements such as oxygen, nitrogen, or fluorine.
• The hydrogen atom acts as a hydrogen bond donor while the element it is bonded to acts as a hydrogen bond acceptor.
• ID arises in mixtures of ionic compounds dissolved in polar solvents.
• The positive end of the polar solvent is attracted to the negative ion and vice versa.

London Dispersion Forces (LDFs)

• Occur in all molecules.
• Induced/temporary dipoles due to electron movement in the electron cloud.
• Polarizability relates to electron cloud distortion easiness, influencing LDF strength.
• Stronger LDFs with more polarizable molecules.

Dipole-Dipole Interactions (DD)

• Exist only in polar molecules with permanent dipoles.
• Molecules align so opposite partial charges attract.

Hydrogen Bonding (HB)

• Strong intermolecular force due to hydrogen bonded to highly electronegative elements like nitrogen, oxygen, or fluorine.
• HB donor is the hydrogen atom, and the elements are HB acceptors.
• Stronger compared to LDF or DD.

Ion-Dipole Interactions (ID)

• Occurs between ionic and polar substances.
• The more polar the solvent, the stronger the attraction.

Phase Changes

• Condensation is gas changing to liquid.
• Vaporization is liquid changing to gas.
• Freezing is liquid to solid.
• Melting is solid to liquid.
• Sublimation is solids directly to gas and vice versa.
• Deposition

Phase Diagrams

• Show conditions of temperature and pressure where phases exist.
• Water and Carbon Dioxide have different phase diagrams due to different intermolecular forces.

Properties of Liquids

• Viscosity is the resistance to flow.
• Stronger IMAFs result in higher viscosity.
• Vapor pressure is the pressure exerted by vapor above the liquid.
• Stronger IMAFs result in lower vapor pressure.
• More volatile liquids have higher vapor pressure.

Solubility

• Like dissolves like.
• Polar solvents dissolve polar or ionic solutes.
• Nonpolar solvents dissolve nonpolar solutes.

Boiling Point

• Methyl fluoride has a higher boiling point than methane due to its polarity and stronger dipole-dipole interactions.
• Being polar contributes to stronger interactions than the weaker LDF forces in methane.

Number of HB donor and acceptor sites in an amino acid.

• Example, serine.
• HB donor sites in serine = 5
• HB acceptor sites in serine = 6