High School Chemistry : Compounds and Bonding

Study concepts, example questions & explanations for High School Chemistry

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Example Questions

Example Question #1 : Help With Vsepr Theory And Geometry

What is the molecular geometry of an ammonia molecule with the formula ?

Possible Answers:

Trigonal bipyramidal

Trigonal planar

Tetrahedral

Trigonal pyramidal

Correct answer:

Trigonal pyramidal

Explanation:

In an ammonia molecule, the nitrogen is bonded to three hydrogen atoms and also has a lone electron pair. This lone pair will repel the three hydrogens out of a planar orientation, which results in a trigonal pyramidal geometry.

Compounds with the general formula AX3 and one lone pair will be trigonal pyramidal.

Compounds with the general formula AX3 and no lone pairs will be trigonal planar.

Compounds with the general formula AX4 and no lone pairs will be tetrahedral.

Compounds with the general formula AX5 and no lone pairs will be trigonal bipyramidal.

Example Question #2 : Help With Vsepr Theory And Geometry

What is the bond angle found in a methane molecule with the formula ?

Possible Answers:

Correct answer:

Explanation:

Methane has a carbon atom attached to four hydrogen atoms. In order to be as far as possible from one another, the hydrogen atoms will orient themselves around the carbon in a tetrahedral geometry. Tetrahedral geometries have bond angles of  between each constituent.

Example Question #1 : Help With Vsepr Theory And Geometry

Which of the following choices correctly describes the VSEPR shape of the water molecule, ?

Possible Answers:

Tetrahedral

Trigonal bipyramidal

Linear

None of the answer choices correctly describe the VSEPR shape of the water molecule

Trigonal planar

Correct answer:

Tetrahedral

Explanation:

In the water molecule, there are four electron pairs. Two of them are bonded and two of them are lone pairs. This causes the water molecule to have a tetrahedral shape (it is important to note that it is a bent tetrahedral shape due to the two lone pairs).

Example Question #1 : Help With Vsepr Theory And Geometry

Which of the following compounds has a bent shape according to VSEPR theory?

Possible Answers:

Correct answer:

Explanation:

Generally, a central atom bound to two peripheral atoms will result in a linear shape, as exemplified by carbon dioxide. Exceptions come into play, however, with the introduction of lone pairs of electrons. These lone pairs carry a negative charge, pushing other atoms (and their negatively-charged electrons) farther away. In water, the central oxygen atom is bound to two hydrogen atoms and carries two lone pairs of electrons. As a result, the lone pairs propel the hydrogen atoms away from the linear structure, "bending" the molecule. The result is known as a bent molecular geometry, according to VSEPR theory. Any molecule in which the central atom is bound to two atoms and carries two lone pairs will result in a bent shape.

Carbon dioxide and cyanide are both linear. Ammonia is trigonal pyramidal. Methane is tetrahedral.

Example Question #51 : Compounds And Bonding

Which of the following cannot participate in hydrogen bonding?

Possible Answers:

All of these can participate in hydrogen bonding

Fluorine

Chlorine

Nitrogen

Oxygen

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 #1 : 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 #11 : Intermolecular Forces

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

Possible Answers:

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

Dipole-dipole attraction and ionic bonding

London dispersion forces and hydrogen bonding

London dispersion forces only

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:

None of these answers

Hydrogen bonds

Ionic bonds

Double bonds

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 #5 : Help With Intermolecular Forces

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

Possible Answers:

London dispersion forces

Hydrogen bonding

Heisenberg bonding

Ionic bonding

Covalent 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 #6 : 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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