Ch.12 - Intermolecular Forces (IMFs)

Crystalline solid

atoms are well-ordered in a 3D array

Amorphous solid

atoms have no long-range order

Which states of matter can be compressed?

liquids and gasses

London dispersion force (LDF)

present in all molecules; result from e- distribution fluctuations within molecules and atoms

instantaneous/temporary dipole

momentary charge separation from e- distribution in LDF

LDF increases with:

• inc molar mass

• longer molecules

• larger e- clouds

Dipole-dipole force

present in polar molecules; pos end of permanent dipole attracts neg end of another

Hydrogen bonding

H bonded to F, O, or N

Ion-dipole force

ionic compound attracted to polar compound

Order of increasing IMFs

LDF < dipole-dipole force < hydrogen bonding < ion-dipole force

Surface tension

tendency of liquids to minimize surface area

Surface tension increases with

increasing IMFs

Viscosity

liquid’s resistance to flow

Viscosity increases with

• increasing IMFs

• decreasing temp

Capillary action

ability for liquid to flow against gravity

Cohesive forces

attraction between molecules in a liquid

Adhesive forces

attraction between molecules and surface of a tube

What happens when adhesion > cohesion?

draws liquid up tube, concave shape

What happens when adhesion < cohesion?

liquid drops to level below surrounding liquid, convex shape

Vaporization

liquid to gas

Volatile

liquids that evaporate easily

Vaporization increases with

• inc temp

• inc surface area

• dec strength of IMFs

Heat of vaporization (ΔHvap)

amount of heat needed to vaporize 1 mol of liquid to gas

Dynamic equilibrium

when rate of condensation and rate of vaporization are equal

Vapor pressure

pressure of gas in dynamic equilibrium with its liquid

Vapor pressure increases with

• dec IMFs

• inc temp

What is vapor pressure independent of?

surface area

Boiling point

temp that a liquid’s vapor pressure equals external pressure

Supercritical fluid

commingling of liquid and gas states

Critical temp (Tc)

temp that transition to supercritical fluid occurs

Critical pressure (Pc)

pressure that transition to supercritical fluid occurs