High School Chemistry : Help with Intermolecular Forces

Study concepts, example questions & explanations for High School Chemistry

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Example Questions

Example Question #1 : Help With Intermolecular Forces

Which of the following cannot participate in hydrogen bonding?

Possible Answers:

Fluorine

Chlorine

Oxygen

Nitrogen

All of these can participate in hydrogen bonding

Correct answer:

Chlorine

Explanation:

Hydrogen bonds are intermolecular forces between hydrogens and adjacent molecules. These adjacent molecules must contain either fluorine, oxygen, or nitrogen, the three most electronegative atoms. These electronegative atoms pull electrons away from the bonded hydrogen, giving it a small positive charge and giving themselves a slightly negative charge. When the positive hydrogen of one molecule come close to a negative charge on another, the opposite charges attract and pull the molecules close together to form a hydrogen bond. The hydrogen must be bonded to oxygen (-OH), fluorine (HF), or nitrogen (-NH) to have this charging effect.

Example Question #2 : Help With Intermolecular Forces

Which of the following molecules cannot participate in hydrogen bonding?

Possible Answers:

Correct answer:

Explanation:

Hydrogen bonding takes place when a hydrogen atom is attracted to a highly electronegative atom in another molecule. Hydrogen bonding takes place between hydrogen and either nitrogen, oxygen, or fluorine. Carbon has an electronegativity similar to hydrogen's, and will not hydrogen bond with hydrogens in other molecules.

Only molecules with -OH, -FH, or -NH groups can form hydrogen bonds.

Example Question #3 : Help With Intermolecular Forces

What intermolecular forces can be found in a molecule of ethene?

Possible Answers:

London dispersion forces and hydrogen bonding

London dispersion forces only

Dipole-dipole attraction and ionic bonding

London dispersion forces, hydrogen bonding, and dipole-dipole attraction

London dispersion forces and dipole-dipole attraction

Correct answer:

London dispersion forces only

Explanation:

Ethene is an organic molecule composed of two carbon atoms, joined by a double bond, and four hydrogen atoms.

Ethene, like all molecules, exhibits London dispersion forces. This molecule, however, has no net dipole moment, so it will not exhibit dipole-dipole attraction. Also, even though it contains hydrogens, it does not exhibit hydrogen bonding. To exhibit hydrogen bonding, the hydrogen atoms must be attached to more electronegative atoms, namely nitrogen, fluorine, or oxygen. Finally, ionic bonding is only present in ionic compounds, not organic compounds.

Example Question #4 : Help With Intermolecular Forces

Which of the following intermolecular forces is broken when water is boiled?

Possible Answers:

Ionic bonds

Double bonds

Hydrogen bonds

None of these answers

Covalent bonds

Correct answer:

Hydrogen bonds

Explanation:

Intermolecular forces are transient forces between two separate molecules. Water is a polar molecule. The oxygen atom carries a slight positive charge, while the hydrogen atoms carry slight negative charges. This is the result of the large difference in electronegativity between oxygen and hydrogen. When two water molecules are next to each other, the partially positive hydrogen will be attracted to the partially negative oxygen. This attraction is known as a hydrogen bond.

Ionic bonds, covalent bonds, and double bonds are all intramolecular forces. These are stable bonds between atoms that establish the identity of the molecule. Breaking any of these bonds would alter the identity of the compound.

Example Question #1 : Help With Intermolecular Forces

Water has a higher boiling point than hydrogen sulfide due to which type of bonding?

Possible Answers:

Ionic bonding

London dispersion forces

Hydrogen bonding

Covalent bonding

Heisenberg bonding

Correct answer:

Hydrogen bonding

Explanation:

Hydrogen bonding occurs between a hydrogen atom on one molecule and a very electronegative atom—namely oxygen, nitrogen, or fluorine—on a neighboring molecule. This electrostatic force results in a stronger intermolecular bond than would otherwise be present without the hydrogen bond. A stronger intermolecular bond results in a higher boiling point.

Water (H2O) exhibits hydrogen bonding between the hydrogen of one water molecule and the oxygen of another water molecule. Since sulfur is not as electronegative as oxygen, hydrogen sulfide (H2S) does not exhibit hydrogen bonding. This is the reason why water is a liquid at room temperature, while hydrogen sulfide is a gas.

Wrong answers explained: Neither water nor hydrogen sulfide has ionic bonds. Both have covalent bonds and London dispersion force, but this does not explain why water's boiling point is higher. Heisenberg bonding does not exist and is a misleading answer option.

Example Question #2 : Help With Intermolecular Forces

Which of the following compounds will exhibit hydrogen bonding?

Possible Answers:

Correct answer:

Explanation:

When hydrogen is bound to either fluorine, oxygen, or nitrogen, the hydrogen atom carries little of the electron density of the covalent bond. This partially positively charged hydrogen atom may interact with the partial negative charge located on adjacent electronegative atoms such as F, N, or O on adjacent molecules. Note that hydrogen bonds are intermolecular forces, not intramolecular. This means that hydrogen bonds form between two separate molecules. They plan an important role in the chemistry of water, and other compounds that exhibit hydrogen bonding. 

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