AP Chemistry: Intermolecular Forces and Properties

Intermolecular Forces (IMFs)

Attractive forces between separate molecules, unlike intramolecular forces which exist within a molecule.

London Dispersion Forces (LDF)

Weak intermolecular forces that exist between all molecules and atoms due to temporary dipoles.

Polarizability

The ease with which an electron cloud can be distorted; larger electron clouds are more polarizable.

Dipole-Dipole Forces

Forces that occur between molecules with permanent dipoles, where the positive end of one molecule attracts the negative end of another.

Hydrogen Bonding

A strong type of dipole-dipole attraction that occurs when hydrogen is bonded to N, O, or F.

Ion-Dipole Forces

Attractive forces that occur between an ionic compound and a polar solvent.

Strength Hierarchy of IMFs

LDF < Dipole-Dipole < Hydrogen Bonding < Ion-Dipole < Covalent/Ionic Bonds.

Ionic Solids

Solids composed of ions held together by ionic bonds within a 3D lattice.

Molecular Solids

Solids made up of distinct neutral molecules held together by intermolecular forces.

Network Covalent Solids

Solids composed of atoms connected in a vast network through covalent bonds.

Metallic Solids

Solids consisting of metal cations surrounded by a sea of delocalized electrons.

Vapor Pressure

The pressure exerted by a gas in equilibrium with its liquid phase; influenced by the strength of IMFs.

Boiling Point

The temperature at which vapor pressure equals atmospheric pressure; higher with stronger IMFs.

Viscosity

The resistance of a liquid to flow; higher with stronger intermolecular forces.

Surface Tension

The energy required to increase the surface area of a liquid; stronger IMFs lead to higher surface tension.

Kinetic Molecular Theory (KMT)

A model that explains the behavior of ideal gases based on particle motion and interactions.

Maxwell-Boltzmann Distribution

A graph showing the distribution of particle speeds in a gas sample, affected by temperature and molar mass.

Ideal Gas Equation

PV = nRT, representing the relationship between pressure, volume, moles, and temperature of an ideal gas.

Dalton's Law of Partial Pressures

States that the total pressure of a gas mixture equals the sum of the partial pressures of its components.

Real Gases Deviations

Real gases deviate from ideal behavior at high pressures and low temperatures when KMT assumptions break down.

Molarity (M)

Concentration measured as moles of solute divided by liters of solution.

'Like Dissolves Like'

The principle that polar solvents dissolve polar or ionic solutes, and nonpolar solvents dissolve nonpolar solutes.

Distillation

A separation technique that uses differences in boiling points to separate liquids.

Chromatography

A technique for separating components of a mixture based on their polarity.

Microwave Radiation

Electromagnetic radiation that causes molecular rotation.

Infrared (IR) Radiation

Radiation that causes molecular vibration, useful for identifying functional groups.

UV/Vis Radiation

Radiation that causes electronic transitions in molecules.

Beer-Lambert Law

A law that relates absorbance to concentration and path length: A = εbc.

Intermolecular Properties

The properties observed in substances based on the type and strength of their intermolecular forces.

Covalent Bonds

Strong chemical bonds that exist within molecules, significantly stronger than IMFs.

Brittleness in Ionic Solids

The tendency of ionic solids to shatter when layers shift due to repulsion.

Conductivity of Metallic Solids

Excellent electrical conduction due to the presence of delocalized electrons.

Network Solid vs. Molecular Solid

Network solids, like diamond, have very high melting points, unlike molecular solids such as CO2.

Phase Change Temperature

Temperature does not change during a phase transition; energy goes into breaking IMFs.

Temperature for Gas Laws

Always use Kelvin for temperature in gas law calculations.

Dissolving Process

Dissolving is not melting; it involves dissociation of solute into ions or molecules.

Soft/Brittle Properties of Molecular Solids

Molecular solids tend to be soft or brittle due to weaker intermolecular forces.

Hydrogen Bonding Characteristics

Unique strength among IMFs due to large dipoles when hydrogen is bonded to highly electronegative atoms.

Viscosity and IMFs

The resistance of a liquid to flow increases with stronger intermolecular forces.

Ion-Dipole Importance

Explains why ionic salts dissolve in polar solvents like water.

Effect of Temperature on Gases

As temperature increases, particle speed and distribution in gases also increase.

Elastic Collisions in Gases

Collisions between gas particles that conserve kinetic energy.

Separation Techniques in Chemistry

Methods utilized to isolate compounds based on differences in physical and chemical properties.

Difference Between Polar and Nonpolar Solvents

Polar solvents dissolve polar/ionic substances while nonpolar solvents dissolve nonpolar substances.

Strongest Intermolecular Force

Ion-Dipole forces are stronger than hydrogen bonds due to the effective interaction between charges.

Energy in Phase Changes

Energy is absorbed or released during phase changes; no temperature change occurs.

Atom vs Molecule in Solids

Atoms in network solids are bonded in larger structures, while distinct neutral molecules make up molecular solids.

Lattice Structure of Ionic Solids

Represents the arrangement of cations and anions connected by ionic bonds in a repeating pattern.