Chapter 11 - Intermolecular Forces

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88 Terms

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States

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

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Gases

Highly compressible & assume shape/volume of their container.

Molecules are far apart and do not interact much.

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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.

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Solids

Incompressible and have a definite shape/volume.

Molecules are packed closely together (extremely rigidly).

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condensed

Solids and liquids are _____________ phases.

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Crystalline

Solids with highly ordered structures.

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cooling or compressing

Gas → Liquid → solid

This conversion can be achieved by…

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heating or reducing pressure

Solid → Liquid → gas

This conversion can be achieved by…

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Intermolecular Forces

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

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Intramolecular Forces

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

[These do NOT break with state changes]

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intramolecular

Which is stronger, Intermolecular or Intramolecular?

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direct

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

BP+, AF+

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direct

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

MP+, AF+

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bigger charges, closer molecules

Why are intramolecular forces stronger?

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Dispersion

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

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direct

Relationship between dipole moment and boiling point/forces.

DM+, BP/AF +

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momentary dipole

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

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Polarizability

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

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direct

Relationship between polarizability and dispersion forces.

P+, DF+

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

W/A +, DF+

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smaller

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

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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.

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higher

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

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dipole moment

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

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increasing

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

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direct

Relationship between polarity and intermolecular attractions.

P+, IA+

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Hydrogen Bonding

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

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high

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

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small electronegative element

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

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unshared electron pair

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

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weaker

Hydrogen bonds are much ____________ than ordinary chemical bonds.

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Ion-Dipole Forces

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

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direct

Relationship between magnitude, ionic charge, and dipole magnitude.

M+, IC+, DM+

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dispersion forces

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

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polar

Dipole-dipole forces are found ONLY in ___________ molecules.

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

List the 4 Intermolecular forces in order of increasing strength:

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dispersion forces

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

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stronger

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

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higher

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

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Viscosity

The resistance of a liquid to flow.

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direct

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

B+, V+

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direct

Relationship between intermolecular force strength and viscosity.

IF+, V+

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indirect

Relationship between viscosity and temperature.

V+, T-

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Surface Tension

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

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higher

Stronger intermolecular forces cause ____________ surface tension.

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cohesive forces

Intermolecular forces that bind molecules to one another.

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adhesive forces

Intermolecular forces that bond molecules to a surface.

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greater

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

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weaker

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

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liquid stops rising

What happens when cohesive forces = adhesive forces?

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Capillary Action

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

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Endothermic

Reactions where energy is ADDED (absorbs energy from surroundings)

BREAKING bonds!!

Reactions generally get cold.

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Exothermic

Reactions where energy in RELEASED to the surroundings.

MAKING/FORMING bonds!!

Reactions generally get warm.

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exothermic

Gas → Liquid → Solid [endo/exo?]

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endothermic

Solid → Liquid → Gas [endo/exo?]

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vaporization

Which is larger, ∆H(fus) or ∆H(vap)?

(think about intermolecular attractions)

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Sublimation, endothermic

Solid → Gas [name, endo/exo]

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Fusion, endothermic

Solid → Liquid [name, endo/exo]

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Vaporization, endothermic

Liquid → Gas [name, endo/exo]

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Deposition, exothermic

Gas → Solid [name, endo/exo]

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Condensation, exothermic

Gas → Liquid [name, endo/exo]

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Freezing, exothermic

Liquid → Solid [name, endo/exo]

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Heating curve

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

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No

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

(think about intermolecular bonds)

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Supercooling

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

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Critical Temperature

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

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Critical Pressure

The pressure required for liquefication at this critical temperature.

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higher

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

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Supercritical Fluid

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

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increase

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

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Vapor pressure

The pressure of a vapor

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Dynamic Equilibrium

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

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Vapor Pressure of a liquid

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

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volatile

A liquid that evaporates easily is said to be _____________.

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direct

Relationship between temperature, AKE, and volatility.

T+, AKE+, V+

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indirect

Relationship between Intermolecular Forces and Vapor Pressure.

IF+, VP-

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indirect

Relationship between boiling point and volatility.

BP+, V-

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Boiling point

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

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Normal boiling point

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

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increases

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

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increase temperature, decrease pressure

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

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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.

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Vapor Pressure Curve

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

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Critical Point

Point representing the critical temperature and pressure for the gas.

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Sublimation curve

Curve separating the solid and gas phases.

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Melting curve

Curve separating the solid and liquid phases.

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Normal melting point

Melting point at 1 atm

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Triple point

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