Chapter 11 - Intermolecular Forces

States

States

______________ depend on the balance between kinetic energies of particles and interparticle energies of attraction.

Gases

Highly compressible & assume shape/volume of their container.

Molecules are far apart and do not interact much.

Liquids

Almost incompressible and assume the shape, but not volume, of their container.

Molecules held more closely together, but not so rigid that the molecules cannot move.

Solids

Incompressible and have a definite shape/volume.

Molecules are packed closely together (extremely rigidly).

condensed

Solids and liquids are _____________ phases.

Crystalline

Solids with highly ordered structures.

cooling or compressing

Gas → Liquid → solid

This conversion can be achieved by…

heating or reducing pressure

Solid → Liquid → gas

This conversion can be achieved by…

Intermolecular Forces

Forces between molecules that hold them together (many physical properties are caused by these…)

Intramolecular Forces

Forces between bonds (i.e. covalent, ionic, metallic)

[These do NOT break with state changes]

intramolecular

Which is stronger, Intermolecular or Intramolecular?

direct

Boiling point and Attractive Forces have an/a __________ relationship.

BP+, AF+

direct

Melting Point and Attractive Forces have a/an _______________ relationship.

MP+, AF+

bigger charges, closer molecules

Why are intramolecular forces stronger?

Dispersion

Intermolecular force resulting from shifting electron clouds (neutral non-polar atoms and/or molecules).

direct

Relationship between dipole moment and boiling point/forces.

DM+, BP/AF +

momentary dipole

The movement of electrons when attractions happen in Dispersion causes a ____________ ____________.

Polarizability

The ease with which an electron distribution can be deformed (“squashiness” of its electron cloud)

direct

Relationship between polarizability and dispersion forces.

P+, DF+

Relationship between weight/area of a molecule and dispersion forces.

W/A +, DF+

smaller

Dispersion forces between spherical molecules are _____________ than those between more cylindrically shaped molecules (due to more molecular contact).

Dipole-Dipole

Force existing between neutral polar molecules in which there is attraction of the + end of one polar molecule to the - end of another polar molecule.

higher

The ___________ boiling point reflects the dipole-dipole interactions present.

dipole moment

Compounds consisting of atoms with different electronegativities may have a _______________/partial charge caused by electron asymmetry.

increasing

If two molecules have about the same mass/size, then the strength of the intermolecular attractions between them increases with _______________ polarity.

direct

Relationship between polarity and intermolecular attractions.

P+, IA+

Hydrogen Bonding

Intermolecular force containing polar molecules with H-F, H-O, and H-N.

high

Boiling points of compounds with H-F, H-O, and H-N are abnormally _________.

small electronegative element

For Hydrogen Bonding, H must be bonded to a _________ ________________ __________.

unshared electron pair

Also, for Hydrogen Bonding, there must be an _______________ _____________ _________ on a nearby small electronegative ion/atom.

weaker

Hydrogen bonds are much ____________ than ordinary chemical bonds.

Ion-Dipole Forces

Intermolecular force being an interaction between an ion and the partial change on the end of a polar molecule.

direct

Relationship between magnitude, ionic charge, and dipole magnitude.

M+, IC+, DM+

dispersion forces

the strength of ____________ ______________ depends on molecular shapes and molecular weights.

polar

Dipole-dipole forces are found ONLY in ___________ molecules.

dispersion < dipole-dipole < hydrogen bonding < ion-dipole

List the 4 Intermolecular forces in order of increasing strength:

dispersion forces

If the molecules of two substances have similar molecular weights and shapes, ____________ _________ will be similar in magnitude.

stronger

The greater the molecular polarity, the _____________ the intermolecular forces.

higher

Intermolecular attractive forces will generally be greater in the substance with the ______________ molecular weight.

Viscosity

The resistance of a liquid to flow.

direct

Relationship between number of branches and viscosity (because of entanglement)

B+, V+

direct

Relationship between intermolecular force strength and viscosity.

IF+, V+

indirect

Relationship between viscosity and temperature.

V+, T-

Surface Tension

The amount of energy required to increase the surface area of a liquid by a unit amount.

higher

Stronger intermolecular forces cause ____________ surface tension.

cohesive forces

Intermolecular forces that bind molecules to one another.

adhesive forces

Intermolecular forces that bond molecules to a surface.

greater

If adhesive forces are _____________ than the cohesive forces, the meniscus is u-shaped (concave up).

weaker

If adhesive forces are _____________ than the cohesive forces, the meniscus is concave down.

liquid stops rising

What happens when cohesive forces = adhesive forces?

Capillary Action

The rise of liquids up very narrow tubes (climbs until adhesive and cohesive forces are balanced).

Endothermic

Reactions where energy is ADDED (absorbs energy from surroundings)

BREAKING bonds!!

Reactions generally get cold.

Exothermic

Reactions where energy in RELEASED to the surroundings.

MAKING/FORMING bonds!!

Reactions generally get warm.

exothermic

Gas → Liquid → Solid [endo/exo?]

endothermic

Solid → Liquid → Gas [endo/exo?]

vaporization

Which is larger, ∆H(fus) or ∆H(vap)?

(think about intermolecular attractions)

Sublimation, endothermic

Solid → Gas [name, endo/exo]

Fusion, endothermic

Solid → Liquid [name, endo/exo]

Vaporization, endothermic

Liquid → Gas [name, endo/exo]

Deposition, exothermic

Gas → Solid [name, endo/exo]

Condensation, exothermic

Gas → Liquid [name, endo/exo]

Freezing, exothermic

Liquid → Solid [name, endo/exo]

Heating curve

Plot of temperature change (y) versus heat added (x).

No

Does adding heat cause a temperature change during a phase change?

(think about intermolecular bonds)

Supercooling

______________ occurs when a liquid is cooled below its freezing point and still remains a liquid.

Critical Temperature

The highest temperature at which a substance can exist as a liquid.

Critical Pressure

The pressure required for liquefication at this critical temperature.

higher

The greater the intermolecular forces, the _____________ the critical temperature.

Supercritical Fluid

A substance at temperatures and pressures higher than its critical temperature and pressure in a state.

increase

As the number of molecules in the gas phase ______________, some of the gas phase molecules strike the surface and return to the liquid.

Vapor pressure

The pressure of a vapor

Dynamic Equilibrium

A condition in which two opposing processes occur simultaneously at equal rates.

Vapor Pressure of a liquid

The pressure exerted by a vapor when the liquid and vapor are in dynamic equilibrium.

volatile

A liquid that evaporates easily is said to be _____________.

direct

Relationship between temperature, AKE, and volatility.

T+, AKE+, V+

indirect

Relationship between Intermolecular Forces and Vapor Pressure.

IF+, VP-

indirect

Relationship between boiling point and volatility.

BP+, V-

Boiling point

The temperature at which the external pressure at the liquid surface equals the vapor pressure.

Normal boiling point

The boiling point of a liquid at 760 mm Hg (1 atm).

increases

The temperature of the boiling point ____________ as external pressure increases.

increase temperature, decrease pressure

What are the two ways to get a liquid to boil?

Phase diagram

A plot of pressure (y) versus temperature (x) summarizing all equilibria between phases.

This diagram tells us which phase will exist at a given temperature and pressure.

Vapor Pressure Curve

Curve where, generally, as temperature increases the vapor pressure increases.

Critical Point

Point representing the critical temperature and pressure for the gas.

Sublimation curve

Curve separating the solid and gas phases.

Melting curve

Curve separating the solid and liquid phases.

Normal melting point

Melting point at 1 atm

Triple point

Point representing when the temperature and pressure of ALL THREE phases are in equilibrium.