AP Chemistry - Intermolecular Forces and Properties

intermolecular forces

attractive or repulsive forces caused by partial charges between particles

dipole

having postive and negative ends due to charge separation within the molecule

ion-dipole

attraction of an ion and a polar molecule

Where are ion-dipole forces important?

aqueous solution containing an electrolyte, aqueous salt solutions

dipole-dipole

attraction between postive end of one dipole to negative end of another dipole

hydrogen bonding

a hydrogen atom is polar-covalently bonded to N, O, or F

ion-induced dipole

an ion induces a temporary dipole on a nonpolar molecule

dipole-induced dipole

a dipole induces a temporary dipole on a nonpolar molecule

London dispersion forces

attraction from induced dipole

Where are London dispersion forces present?

in all molecules

liquid state

specific volume but no shape; particles in constant flux

surface tension

amount of force required to break through the surface molecular layer of a liquid

Surface tension increases with

greater molecular force

Viscosity

resistance of liquids to flow

factors that affect viscosity

intermolecular forces, temperature, molecular shape

capillary action

spontaneous rising of a liquid through a narrow tube against the force of gravity

capillary action is caused by

competition between intermolecular forces within the liquid and those between the liquid and the wall

water is called the

universal solvent

heat capacity

heat absorbed to cause temperature to rise

heat of vaporization

heat needed to transform a liquid into a gas

What are some unique properties of water?

ability to dissolve most substances, high heat capacity, high heat of vaporization, ice is less dense than liquid water

solid

substance with a definite volume and shape

amorphous solid

solids without extensive ordering of particles

crystalline solids

regular ordering of particles in a crystal lattice structure

crystal lattice

three-dimensional structure with repeating units

atomic solids

atoms are held in place by London forces; only noble gases form atomic solids

molecular solids

lattices held together by London, dipole-dipole, and hydrogen bonding forces

ionic solids

lattices composed of ions held together by ionic bonding

metallic solids

lattices composed of metal ions held together by metallic bonding

metallic bonding

delocalized and free moving electrons

covalent network solids

covalent bonds joining atoms together in the crystal lattice

phase diagram

graph representing the relationship of a substance’s states of matter to temperature and pressure

critical point

point at which the gas and liquid phases are indistinguishable

triple point

the combination of temperature and pressure at which all three states of matter can exist together

Stronger intermolecular forces mean that is easier to

condense a gas and harder to vaporize a liquid

how does heat of transition relate to intermolecular forces?

stronger intermolecular force means high heats of transition

how does vapor pressure relate to intermolecular forces?

weaker intermolecular forces means higher vapor pressure

intermolecular forces are key in which experiments

separation of components of a mixture

how are melting point and freezing point related?

they are identical

Gas constant (*R*)

0\.08206 L atm mol^-1 K^-1

standard temperature and pressure (STP)

273\.15 K and 1.0 atm

1 atm to mm Hg

760 mm Hg

Gas law

PV=nRT

number of moles equation

n = m/M

density equation

D = m/V

Kinetic Molecular Theory

theory that represents the properties of gas through modeling gas particles at the microscopic level

first postulate of kinetic moleculary theory

gases are composed of very small molecules

second postulate of kinetic molecular theory

the volume of the gas particles is negligible

third postulate of kinetic molecular theory

gas particles are in constant motion

fourth posulate of kinetic molecular theory

gas particles do not attract or repel each other; their collisions are elastic

fifth postulate of kinetic molecular theory

the average kinetic energy of the gas is proportional to the Kelvin temperature

ideal gas

a gas that obeys the Kinetic Molecular Theory

Are there any actual ideal gases?

no

Which gases approach ideal gas behavior?

nonpolar gases at low pressure and high temperature

root mean square speed (µrms)

average velocity of the gas particles

root mean square speed equation

√3RT/M

average kinetic energy formula (per molecule)

KE = 1/2*mv^2*

average kinetic energy per mol of gas

*KE* per mol = 3/2 *RT*

barometer

insturment used to measure atmospheric pressure

how does a barometer work?

a hollow tube is filled with mercury and its open end is immersed in a pool of mercury. gravity pulling the liquid level in the tube down opposing the weight of atmospheric gases forcing liquid upwards stablizes the column at 760 mm at sea level

1 atm to pascal (Pa)

101325 Pa

manometer

an instrument used to measure the gas pressure in a container

Boyle’s law

pressure and volume are invesrsely proportional when temperature and moles are constant

Boyle’s law equation

P1V1=P2V2

Charles’s law

volume and temperature are directly proportional when pressure and moles are constant

Charles’s law equation

V1/T1=V2/T2

Gay-Lussac’s law

pressure and temperature are directly related when volume and moles are constant

Gay-Lussac’s law equation

P1/T1=P2/T2

combined gas law equation

(P1V1)/T1=(P2V2)/T2

Avogadro’s Law equation

V1/n1=V2/n2

Avogadro’s law

volume and moles are directly proportional when pressure and temperature are constant

what is the molar volume of a gas at STP?

22\.4 L mol^-1

ideal gas equation

PV=nRT

Dalton’s law

in a mixture of gases, the total temperature is the sum of the partial pressures

Dalton’s law equation

Ptotal=PA+PB+PC…

XA

mole fraction of gas A

equation for partial pressure from moles and total pressure

PA=(PTotal)(XA)

Graham’s law

defines the relationship of the speed of gas diffusion or effusion and a gas’s molecular mass

diffusion

mixture of gases due to their kinetic energy

effusion

movement of a gas through a tiny opening

Graham’s law equation

r1/r2=√M2/M1

rates of effusion or diffusion and molecular mass are _________ related

inversely

van der Waals equation

(P+an^2/V^2)(V-nb)=nRT

when is the van der Waals equation more helpful?

when the intermolecular forces are stronger

why is the assumption for volume for ideal gases incorrect?

gas molecules have a finite volume which is greater with more gas moles present

why is the assumption for pressure for ideal gases incorrect?

greater attraction lessens the actual pressure

describe an common experiment involving Dalton’s law

adjusting the pressure of a gas sample for the presence of water using a heated tube and an inverted water-filled test tube

describe a common experiment involving Graham’s law

measuring the time required for a sample to effuse

calculating volume requires knowing

the number of gas moles present

solution

homogenous mixture composed of a solvent and one or more solutes

solvent

substance acting as the dissolving medium

examples of non-liquid solvents

nitrogen in our atmosphere, iron in steel

solute

substance that the solute dissolves

what is the principle for dissolution in chemistry

like dissolves like

saturated solution

a solution which the maximum amount of solute per given solvent at a given temperature has been dissolved

unsaturated solution

less than the maximum amount of solute has been dissolved

supersaturated solution

more than the maximum amount of solute has been dissolved

dilute

a solution that has a relatively small amount of solute

concentrated

a solution that has a relatively large amount of solute

molarity

number of moles of solute per liter of solution