AP Chemistry: Unit 3 Summary
3.1 Intermolecular Forces
Intermolecular (IMF): Between molecules (Hydrogen-bond, Dipole-Dipole,
London Dispersion Forces)
Intramolecular (Bonds): Within ONE molecule (Ionic Bonds, Polar-Covalent,
Nonpolar-Covalent)
OPPOSITES ATTRACT! (+) & (-) parts attract each other
Dipole-Dipole Interactions (WEAK)
Occur between two (or more) POLAR molecules
Attractive or repulsive, molecules orient themselves for maximum attraction
Interaction strength is based on the magnitude of the dipole
Greater dipole moment = greater attraction
Opposite ends of dipole attract each other, molecules stay close.
About 1% as strong as covalent/Ionic bonds
Weaker with greater distance
Small role in gases
Dipole-Induced Dipole Interaction
When the dipole of polar molecules interacts with non-polar molecules, the
electrons of non-polar molecules are repelled by the negative of polar
molecules, and non-polar molecules are forced to have a dipole (INDUCED
DIPOLE)
Electrons are dynamically moving in molecules, so the “density” of
electrons can change in a given molecule.
AP Chemistry: Unit 3 Summary 1
, Non-polar Molecules: London Dispersion Forces
Electrons fluctuate in non-polar molecules, creating temporary dipoles
Instantaneous dipoles can induce short-lived dipoles in neighboring
molecules
All molecules exhibit LDF, even polar molecules
The larger the electron cloud, the more polarizable and greater strength of
interaction
Hydrogen Bonding
Special case of dipole-dipole, with an unusual strength of interaction
Technically not a bond, as it occurs between molecules
Only takes place when a hydrogen covalent bonds to a high
electronegative atom (N, O, F) attached to the negative end of the dipole
formed by high electronegativity. (N, O, F)
May occur between two different parts of the same molecule
Ion Dipole Interaction
Interaction between ions and water
Ionic compounds dissolve and dipoles of water interact with ions of the
compound and force them to seperate
Stronger than hydrogen bonds, which accounts for the boiling point
elevation of the solution of an Ionic compound
Interactions Between Molecules
When two polar molecules interact:
Dipole-dipole
When one polar and one non-polar molecule interact:
AP Chemistry: Unit 3 Summary 2
3.1 Intermolecular Forces
Intermolecular (IMF): Between molecules (Hydrogen-bond, Dipole-Dipole,
London Dispersion Forces)
Intramolecular (Bonds): Within ONE molecule (Ionic Bonds, Polar-Covalent,
Nonpolar-Covalent)
OPPOSITES ATTRACT! (+) & (-) parts attract each other
Dipole-Dipole Interactions (WEAK)
Occur between two (or more) POLAR molecules
Attractive or repulsive, molecules orient themselves for maximum attraction
Interaction strength is based on the magnitude of the dipole
Greater dipole moment = greater attraction
Opposite ends of dipole attract each other, molecules stay close.
About 1% as strong as covalent/Ionic bonds
Weaker with greater distance
Small role in gases
Dipole-Induced Dipole Interaction
When the dipole of polar molecules interacts with non-polar molecules, the
electrons of non-polar molecules are repelled by the negative of polar
molecules, and non-polar molecules are forced to have a dipole (INDUCED
DIPOLE)
Electrons are dynamically moving in molecules, so the “density” of
electrons can change in a given molecule.
AP Chemistry: Unit 3 Summary 1
, Non-polar Molecules: London Dispersion Forces
Electrons fluctuate in non-polar molecules, creating temporary dipoles
Instantaneous dipoles can induce short-lived dipoles in neighboring
molecules
All molecules exhibit LDF, even polar molecules
The larger the electron cloud, the more polarizable and greater strength of
interaction
Hydrogen Bonding
Special case of dipole-dipole, with an unusual strength of interaction
Technically not a bond, as it occurs between molecules
Only takes place when a hydrogen covalent bonds to a high
electronegative atom (N, O, F) attached to the negative end of the dipole
formed by high electronegativity. (N, O, F)
May occur between two different parts of the same molecule
Ion Dipole Interaction
Interaction between ions and water
Ionic compounds dissolve and dipoles of water interact with ions of the
compound and force them to seperate
Stronger than hydrogen bonds, which accounts for the boiling point
elevation of the solution of an Ionic compound
Interactions Between Molecules
When two polar molecules interact:
Dipole-dipole
When one polar and one non-polar molecule interact:
AP Chemistry: Unit 3 Summary 2
