Ch. 12: Liquids, Solids, and Molecular Forces

The rate of vaporization increases with:

1. Increasing temperature 2. Increasing surface area 3. Decreasing of the strength of intermolecular forces

The presence of polar bonds in a polyatomic molecule does not guarantee that the molecule as a whole is polar and has a net dipole moment because

1. The molecular geometry 2. The overall dipole moment of a molecule is the vector sum of the individual dipole moments of all the polar bonds within the molecule

why studying intermolecular forces is important?

1. used to explain the physical properties of chemical substances 2. state of matter depends on the magnitude of intermolecular forces that exist between the chemical species making up the matter

Van der Waal forces

London Dispersion and Dipole-Dipole

If two chemical substances differ markedly in their molecular masses, and there is no hydrogen bonding, _____ forces will determine which substance has the stronger intermolecular attractions

London dispersion

______ forces are present in all molecules and atoms

London dispersion

Are caused by fluctuations of the electron distribution within molecules or atoms

London dispersion force

This type of intermolecular force is present between all molecules and atoms

London dispersion force

this force increases with increasing molecular weight

London dispersion force

this force is about the same for molecules of substances having similar molecular masses and shapes

London dispersion force

this force tends to be weak in small molecules but are significant in molecules of high molecular weight

London dispersion force

If two chemical substances have comparable molecular masses and shapes, their _____ will be approximately the same

London dispersion forces

______ operate between all molecules, whether they are polar or nonpolar

London dispersion forces

hydrogen bonding is stronger than _____ and ______ intermolecular forces

London dispersion; dipole-dipole

surface tension

a measure of the net inward force that must be overcome to expand the surface area of a liquid

hydrogen bonding

an attractive force between a hydrogen atom that is bonded to a highly electronegative atom (F, O, or N) of a polar bond of one molecule and the F, O, or N atoms of another molecule

non-polar liquid is miscible in

another non-polar liquid

polar liquid tends to be miscible in

another polar liquid

ion-dipole interactions

are Coulombic attractions between ions (either cation or anion) and polar molecules

intramolecular forces

are present within each individual molecule, are the chemical bonds that join the atoms together

vapor pressure of a liquid

at a given room temperature, is the pressure of the vapor over its liquid when the vapor and its liquid are in dynamic equilibrium

Are weak in small molecules (H2 and He) but can become highly significant in atoms/molecules with high molar masses (Xe, I2, CCl4)

characteristic of London dispersion force

Arise as a result of temporary dipoles (instantaneous and induced) created in atoms or molecules

characteristic of London dispersion force

Caused by fluctuations of electron distribution and not by electronegativity difference

characteristic of London dispersion force

Exhibited by all atoms and molecules, since they all have electrons

characteristic of London dispersion force

intramolecular forces influence the ______ properties of substances

chemical

Results from a competition between two forces:

cohesive and adhesive

The opposite of vaporization is _____ which is exothermic

condensation

Increasing the temperature of a liquid increases the average kinetic energy of molecules and their molecular motion, and results in a _____ in intermolecular forces within the liquid

decrease

Surface tension _____ with increasing temperature

decreases

as molecular force increases London dispersion force ______

decreases

______ force are present in polar molecules

dipole-dipole

the larger the dipole moment the stronger the ______ force

dipole-dipole

Differences in their combined intermolecular forces will be determined by differences in the strengths of the _____ or the existence of _____

dipole-dipole attractions; hydrogen bonding

the molecule acquiring a permanent dipole that is attracted to another identical dipole

dipole-dipole force

They exist between molecules having permanent dipoles (polar molecules)

dipole-dipole forces

The strength of the London Dispersion force depends on the ease with which the electron cloud in a molecule or an atom can be

distorted to produce an instantaneous dipole

If the adhesive forces are weaker than the cohesive forces, the liquid _____ in capillary tube

does not rise

molecules/atoms with larger molecular weights have more ______ dispersed over a larger volumer

electrons

The partial positive charge on one molecule is ______ attracted to the negative charge on the neighboring molecule

electrostatically

he heat of vaporization is always positive because the process is _____

endothermic

a larger electron cloud leads to a ______ London dispersion force

greater

For molecules of approximately the same shape and mass: Polar molecules have ______ melting points/boiling points than non-polar molecules of similar size

higher

Stronger intermolecular forces hold the molecules together and do not allow them to move easily past each other, and leads to ______ viscosity

higher

the stronger the attractive forces between the molecules, the ______ the boiling point will be

higher

the stronger the intermolecular forces are the ______ will be the boiling point of the liquid and the melting point of the solid

higher

HF, H2O, and NH3 all exhibit

hydrogen bonding

molecules exhibiting _____ will have the stronger intermolecular attractions

hydrogen bonding

this force exists between molecules where hydrogen is chemically bonded to fluorine, oxygen, or nitrogen

hydrogen bonding

______ is stronger than dipole-dipole and London dispersion forces

hydrogen bondings

the magnitude of London dispersion forces tend to ______ with increasing molar mass

increase

For molecules of approximately the same shape and mass: The magnitude of the intermolecular forces ______ with increasing polarity

increases

the polarizability increases as the number of electrons in an atom or molecule ______

increases

The vapor pressure of a liquid _____ with increasing temperature because at higher temperatures, molecules have _____ kinetic energy

increases; higher

for nonpolar Noble gases, as molecular mass increases the number of electrons ______ therefore, the strength of the London dispersion forces ______

increases; increases

the creation of an instantaneous dipole or temporary dipole on one molecule causes an _____ to form on another molecule

induced dipole

the creation of an instantaneous dipole or temporary dipole on one molecule causes an _______ to form on another molecule

induced dipole

molecular shape

influence the magnitude of the London dispersion forces for nonpolar compounds with the same molar mass

London dispersion forces are caused by

instantaneous dipole-induced dipole attraction

London dispersion force is the force of attraction that exists between the ______ and ______ dipoles

instantaneous; induced

Surface tension is affected by the magnitude of the _____ and by _____

intermolecular force; temperature

the viscosity of a liquid substance is related to ______ between its molecules and is also affected by ______

intermolecular forces; temperature

Surface tension arises from the net ______ pull that is experienced by _____ causing the surface of a liquid to tighten like an elastic film and thus reducing its surface area

inward; molecules at the surface of a liquid

______ forces are present in solutions of ionic compounds and polar solvents

ion-dipole

Strongest intermolecular force

ion-dipole force

this type attraction force is very strong and is extremely important in the formation of aqueous solution of ionic compounds

ion-dipole forces

viscosity

is the resistance to flow exhibited by all liquids and gases

In liquids where molecules have large attractive intermolecular forces, the surface tension will be _____

large

the larger the dipole moment the _____ the force of attraction

larger

intramolecular forces involve ______ charges interacting at ______ distances

larger; closer

The greater the polarity, the _____ the dipole-dipole forces between the molecules and the ______ the energy needed to pull them apart

larger; higher

non-volatile

liquids that do not vaporize easily

volatiile

liquids that vaporize easily at ordinary temperatures

at room temperature, ______ intermolecular forces result in substances being solid or liquids

moderate to strong

polar molecules contain electron-rich regions having a partial ______ charge and electron-poor regions with a partial ______ charge

negative, positive

a polar liquid is not miscible in a ______ liquid

non-polar

intermolecular forces

occur between one molecule and another neighboring molecule

intermolecular forces affect the ______ properties of substances

physical

Dipole-dipole force exist between ______ molecules

polar

dipole-dipole

polar molecules can attract each other through dipole-dipole forces

A dipole is characterized by its dipole moment which is a

quantitative measure of a dipole

Raising the temperature of a liquid _____ its viscosity

reduces

If the adhesive forces are stronger than the cohesive forces, the liquid _____ in a capillary tube

rises

intermolecular forces involve ______ charges interacting at ______ distances

smaller; greater

London Dispersion forces are weaker in neopentane than in n-pentane because of their nearly ______ shape, leading to a ______ boiling point

spherical, lower

because electrons are moving in atoms or molecules, there will be instances when the electron distribution in an atom or a molecule is not ______

symmetrical

The heat of vaporization is somewhat _____ dependent

temperature

miscibility

the ability to mix completely into another liquid without forming two separate phases

Polarizability (of the molecule or atom)

the ease with which the electron cloud in a molecule or an atom can be distorted

adhesive forces

the forces that attract the molecules of a substance

cohesive forces

the intermolecular forces which cause the molecules of a given substance to be attracted to each other

instantaneous dipole

the presence of the opposite charges leads to the creation of a momentary dipole

capillary action/ capillarity

the rising of a liquid through a small narrow tube against the pull of gravity

The strength of the ion-dipole force depends on

the size and charge of the ion and the magnitude of the dipole moment

CO2 has two polar bonds, but are non-polar because

the two sum to 0, so the molecule is non-polar

The overall dipole moment of a molecule is

the vector sum of the individual dipole moments within the molecule

the electron distribution in a non polar molecule is ______ and ______

uniform; symmetrical

intermolecular forces are ______ than intramolecular forces

weaker

substances that have much ______ intermolecular forces are gases at room temperature

weaker

What is the Cause of Hydrogen Bonding?

when a very electronegative atom (O, N, or F) is bonded to hydrogen, it strongly pulls the bonding electrons toward it