AP Chemistry : Intermolecular Forces

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

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Example Question #1 : Intermolecular Forces

List the following bond types in order of increasing strength: nonpolar covalent bonds, ionic bonds, hydrogen bonds, polar covalent bonds

Possible Answers:

ionic bond, polar covalent bonds, nonpolar covalent bonds, hydrogen bonds

hydrogen bonds, nonpolar covalent bonds, polar covalent bonds, ionic bonds

hydrogen bonds, ionic bonds, polar covalent bonds, nonpolar covalent bonds

nonpolar covalent bonds, polar covalent bonds, hydrogen bonds, ionic bonds

hydrogen bonds, ionic bonds, nonpolar covalent bonds, polar covalent bonds

Correct answer:

hydrogen bonds, ionic bonds, polar covalent bonds, nonpolar covalent bonds

Explanation:

A hydrogen bond is not a proper chemical bond, but the result of dipole-dipole interactions. While they are very chemically important, hydrogen bonds are dynamic, rather than stagnant. This is the least stable type of bond listed.

Covalent bonds are inherently more stable than ionic bonds as electrons are shared between both bound atoms, so the next stronges bond type is the ionic bond.

Chemists distinguish between covalent and ionic bonds for the sake of simplicity, but there is actually a continuum. Polar covalent bonds are on the continuum between pure ionic bonds and pure covalent bonds, so polar covalent bonds have more ionic character than nonpolar covalent bonds, and thus are less stable than nonpolar covalent bonds.

Example Question #8 : Ap Chemistry

Which of the following compounds experiences the greatest intermolecular forces

Possible Answers:

Ammonia

Glucose

Benzyl Alcohol

Ethyl Alcohol

Formaldehyde

Correct answer:

Ammonia

Explanation:

IMF strength is in the order of ion-ion>h-bond>dipole-dipole>van der waals. Of the listed compounds there aren't any that display ion-ion IMF, and only ammonia has h-bonding, making it the one with the strongest forces.

Example Question #1 : Intermolecular Forces

Order the following compounds from lowest boiling point to highest:

He2 (helium gas)

Isobutyl alcohol

Acetone

Water

Possible Answers:

Helium gas, acetone, water, isobutyl alcohol

Acetone, helium gas, isobutyl alcohol, water

Acetone, helium gas, water, isobutyl alcohol

Isobutyl alcohol, water, acetone, helium gas

Correct answer:

Helium gas, acetone, water, isobutyl alcohol

Explanation:

Helium gas will have the lowest boiling point since it is a noble gas and the only intermolecular forces present are dispersion forces, which are the weakest. Acetone has a dipole, so dipole-dipole forces will be present. Water has a dipole and can also hydrogen bond, as can isobutyl alcohol. However, isobutyl alcohol is heavier than water, and will thus have the highest boiling point.

Example Question #1 : Intermolecular Forces

Put the following in order from greatest to least intermolecular forces:

I. H2O

II. LiOH

III. CO2

Possible Answers:

I>II>III

III>I>II

I>III>II

II>I>III

II>III>I

Correct answer:

II>I>III

Explanation:

LiOH displays ion-dipole IMF, H2displays hydrogen bonding, and CO2 displays dipole-dipole. Ion-dipole is greater than hydrogen bonding as an IMf, and hydrogen bonding is greater than dipole-dipole.

Example Question #4 : Intermolecular Forces

Put the following intermolecular forces in order of decreasing strength:

 

London dispersion forces; hydrogen bonds; dipole-dipole interactions; ion-dipole interactions

Possible Answers:

Hydrogen bonds

ion-dipole interactions

dipole-dipole interactions

London dispersion forces

Dipole-dipole interactions

Hydrogen bonds

Ion-dipole interactions

London dispersion forces

Hydrogen bonds

dipole-dipole interactions

London dispersion forces

Ion-dipole interactions

ion-dipole interactions

hydrogen bonds

dipole-dipole interactions

London dispersion forces

Correct answer:

ion-dipole interactions

hydrogen bonds

dipole-dipole interactions

London dispersion forces

Explanation:

Ion-dipole forces are the forces responsible for the solvation of ionic compounds in aqueous solutions, and are the strongest of the intermolecular foces. Hydrogen bonding is the second strongest intermolecular force, followed by dipole-dipole interactions. London dispersion forces are present in all solutions, but are very small and the weakest of the intermolecular forces.

Example Question #2 : Intermolecular Forces

Which of the following intermolecular forces account for the fact that noble gases can liquefy?

Possible Answers:

Hydrogen bonding

Dispersion forces

Dipole dipole interactions

Ion dipole interactions

Correct answer:

Dispersion forces

Explanation:

Noble gases are uncharged and do not have polar covalent bonds or dipole moments. The only force that could apply to them are dispersion forces.

Example Question #1 : Intermolecular Forces

Which of the following is most similar to hydrogen bonding?

Possible Answers:

A negatively charged chlorine anion in solution will attract nearby positively charged Lithium cations.

Water completely dissolves certain salts, like NaCl.

The slightly negatively charged sulfur atoms in H_2S are attracted to the slightly positively charged  hydrogen atom of a nearby H_2S molecule.

The chlorine bound to carbon in dichloromethane will slightly attract positive charged particles.

Two methane molecules are attracted to one another because of temporary dipoles.

Correct answer:

The slightly negatively charged sulfur atoms in H_2S are attracted to the slightly positively charged  hydrogen atom of a nearby H_2S molecule.

Explanation:

The choice "The slightly negatively charged sulfur atoms in H_2S are attracted to the slightly positively charged  hydrogen atom of a nearby H_2S molecule" is exactly analogous to hydrogen bonding in water.

"Two methane molecules are attracted to one another because of temporary dipoles" describes London dispersion forces.

While "A negatively charged chlorine anion in solution will attract nearby positively charged Lithium cations" may sound like hydrogen bonding, it is more descriptive of  interactions between any charged particles, not charged particles within the same molecule.

"Water completely dissolves certain salts, like NaCl" does not describe bonding at all.

While "The chlorine bound to carbon in dichloromethane will slightly attract positive charged particles" sounds promising, the slight charges are not on the same molecule.

 

 

 

Example Question #3 : Intermolecular Forces

Methanol (H3COH) exhibits all of the following intermolecular forces EXCEPT __________.

Possible Answers:

Dipole-dipole interactions

Ionic bonding

London dispersion forces

Hydrogen bonding

Correct answer:

Ionic bonding

Explanation:

Methanol is not an ionic molecule and will not exhibit intermolecular ionic bonding.

Methanol is polar, and will exhibit dipole interactions. It also contains the -OH alcohol group which will allow for hydrogen bonding.

Example Question #4 : Intermolecular Forces

Which of the following intermolecular forces creates the strongest relative attraction?

Possible Answers:

Dipole-dipole interactions

Dispersion forces

Dipole-ion interactions

Hydrogen bonding

Correct answer:

Dipole-ion interactions

Explanation:

Dipole-ion interactions (an attraction between an ion and a neutral, but polar atom) are the strongest intermolecular forces listed. Ion-ion forces (attraction between two ions) are the strongest interactions overall.

Hydrogen bonding, an attraction between a hydrogen atom and a highly electronegative atom like fluorine, oxygen, or nitrogen, is the second strongest interaction listed.

The third strongest listed is dipole-dipole interactions, an attraction between two polar molecules, followed by dispersion forces, temporary shifts in the electrons of a molecule.

Example Question #5 : Intermolecular Forces

Which intermolecular force is responsible for the high surface tension of water?

Possible Answers:

Covalent bonding

Van der Waals forces

Hydrogen bonding

Dispersion forces

Correct answer:

Hydrogen bonding

Explanation:

Hydrogen bonding is what holds the hydrogen in one molecule of water to the oxygen in another molecule. Surface tension is a measure of the difficulty to disturb the surface of a liquid. The strong intermolecular connections created by hydrogen bonding makes it hard to disrupt adjacent molecules and break the water surface.

Most key properties of water are attributed to its hydrogen bonding.

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