AP Chemistry : Properties of Compounds

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

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Example Question #1 : Properties Of Compounds

Which of the following compounds has the highest boiling point?

Possible Answers:

Correct answer:

Explanation:

Intermolecular forces can be used to explain chemical properties, including boiling point. The only intermolecular force present in all of these hydrocarbons is London-dispersion forces. Dispersion forces have a greater impact on molecules with a greater molecular weight. As such, we can identify the most massive molecule as the one with the highest boiling point.

Of our given answer options, butane , is the largest and will have the highest boiling point.

Example Question #2 : Properties Of Compounds

Which of the following represents the least polar bond?

Possible Answers:

Hydrogen bonded to chlorine

Hydrogen bonded to sulfur

Hydrogen bonded to oxygen

Hydrogen bonded to fluorine

Hydrogen bonded to carbon

Correct answer:

Hydrogen bonded to carbon

Explanation:

Polarity can be approximated by knowing the electronegativity differences between bonding atoms. The greater the difference in electronegativities between atoms, the greater the polarity.

There is a periodic table trend that electronegitivity decreases as you move leftward and down on the table. Since all the possible answers have hydrogen, you should examine the relative electronegativities of carbon, sulfur, chlorine, oxygen, and fluorine. Since carbon is closest to hydrogen on the periodic table, it has the smallest difference in electronegativity to hydrogen. The molecule with the smallest electronegativity difference will be the least polar; thus, we can determine that the bond between hydrogen and carbon will be least polar.

Bonds between hydrogen and oxygen or fluorine are actually so polar that these molecules can form hydrogen bonds, a type of intermolecular force dependent on polarity. Hydrogen bonded to sulfur or chlorine will be less polar than when bonded to fluorine or oxygen, but will still be significantly more polar than a bond with carbon.

Example Question #3 : Properties Of Compounds

Which of the following is the strongest intermolecular force between a molecule of  and a molecule of ?

Possible Answers:

Covalent bonding

Ion-dipole interactions

Dipole-dipole interactions

London dispersion forces

Hydrogen bonding

Correct answer:

London dispersion forces

Explanation:

Let's first examine the molecules and their bond polarities.  has polar bonds between hydrogen and oxygen (capable of hydrogen bonding), as well as an overall polar structure.  has polar bonds between carbon and chlorine, but due to symmetry has an overall nonpolar structure. As a result, carbon tetrachloride will be unable to participate in any dipole interactions, as the molecule has zero net dipole. This leaves London dispersion forces as the only possible interaction between these two molecules.

Note that covalent bonding is present in each individual molecules as an intramolecular force, but is not possible as an intermolecular force. The water molecules will form hydrogen bonds with each other, but will not do so with the carbon tetrachloride molecules.

Example Question #4 : Properties Of Compounds

Which of the following elements has the smallest atomic radius?

Possible Answers:

Lead

Silver

Molybdenum

Tellurium

Tungsten

Correct answer:

Tellurium

Explanation:

There are two applicable periodic table trends for this question. The first is that atomic radius of elements increases as you move down the periodic table. The second is that atomic radius of elements decreases as you move rightward across the periodic table. This means that the atom with the smallest atomic radius should be the upper-right most element on the periodic table. Among the given answer options, that element is tellurium.

Example Question #5 : Properties Of Compounds

Which of the following is an alkaline earth metal?

Possible Answers:

Correct answer:

Explanation:

Alkaline earth metals are in group II of the periodic table. Of the given answer options, strontium (Sr) is the only element in group II.

Rubidium (Rb) is an alkali metal (group I). Iron (Fe) is a transition metal. Iodine (I) and bromine (Br) are halogens.

Example Question #6 : Properties Of Compounds

Which of the following elements as the least attraction for electrons?

Possible Answers:

Correct answer:

Explanation:

There is a periodic table trend that electronegativity decreases as you move leftward and downward on the table. The lower-leftmost element among the answer options is hafnium (Hf).

Example Question #7 : Properties Of Compounds

Which of the following molecule pairs will exhibit hydrogen bonding?

Possible Answers:

All of these will exhibit hydrogen bonding

Correct answer:

All of these will exhibit hydrogen bonding

Explanation:

Hydrogen bonding occurs between a hydrogen atom and a flourine, nitrogen, or oxygen atom with exposed lone pairs. All of the molecules presented are capable of hydrogen bonding.

Example Question #8 : Properties Of Compounds

Which of the following molecules is the most polar?

Possible Answers:

Correct answer:

Explanation:

 is the only polar molecule among the possible answers. If you knew the electronegativity values of oxygen of hydrogen, you could calculate that the electronegativity difference is greater than 0.7, indicating a polar molecule. You could have also drawn the Lewis structure of . The bent shape of the molecule, despite the atomic symmetry, also indicates polarity due to the presence of two lone pairs. The lone pairs will give the oxygen atom a slight negative dipole, leading to a slight positive dipole on each hydrogen atom.

Q4

*Note: this diagram shows only one of oxygen's lone pairs, when it does in fact have two.

Example Question #9 : Properties Of Compounds

Which of the following group 17 elements has the lowest first ionization energy?

Possible Answers:

Correct answer:

Explanation:

There is a periodic table trend that first ionization energy increases as you move up a group. The element situated lowest in group 17 (the halogens) is astatine (At); therefore, it will have the smallest first ionization energy.

The strongest trend for first ionization energy is an increase as one moves upward within a group, however, first ionization energy also increase to the right across a period.

Example Question #10 : Properties Of Compounds

1

Each circle represents an atom and each different color represents a different kind of atom. If two atoms are touching then they are bonded together as a compound. 

Which of the following describes the contents of the given image?

Possible Answers:

Mixture of Compounds and Elements

Mixture of Compounds

Mixture of Elements

Compound

Element

Correct answer:

Compound

Explanation:

This picture represents just one compound. Each individual molecule is identical to the next.

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