Molecules and Compounds - GRE Subject Test: Chemistry
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Which is not a property of covalent compounds?
Which is not a property of covalent compounds?
The incorrect statement is a property of ionic compounds rather than covalent. Recall that electronegativity is a measure of the ability of an atom to draw electrons to itself. Ionic compounds are formed by elements with very different electronegativities, since elements with different electronegativities will tend to form positive and negative ions (that is, they give away or gain electrons easily). In contrast, covalent bonds are formed by elements which are close in electronegativity and could exist as stable free molecules. All other statements are true of covalent compounds.
The incorrect statement is a property of ionic compounds rather than covalent. Recall that electronegativity is a measure of the ability of an atom to draw electrons to itself. Ionic compounds are formed by elements with very different electronegativities, since elements with different electronegativities will tend to form positive and negative ions (that is, they give away or gain electrons easily). In contrast, covalent bonds are formed by elements which are close in electronegativity and could exist as stable free molecules. All other statements are true of covalent compounds.
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2-butyne contains all of the following types of bonds except __________.
2-butyne contains all of the following types of bonds except __________.
2-butyne has the following chemical structure.
The end carbons have 
hybridization (form single bonds only), while the middle two carbons have 
hybridization (involved in a triple bond). There are no 
hybridized carbons in this molecule.
2-butyne has the following chemical structure.
The end carbons have
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The degree of unsaturation for ephedrine (shown below) is __________.
The degree of unsaturation for ephedrine (shown below) is __________.
The degree of unsaturation is equal to the number of rings plus the number of pi bonds in a molecule. Ephedrine has one ring and three pi bonds, so its degree of unsaturation is four.
To arrive at this answer, one could also use the formula below, where 
is the number of carbon atoms, 
is the number of hydrogen atoms, 
is the number of halogen atoms, and 
is the number of nitrogen atoms.
For ephedrine, 
, 
, 
, and 
.
The degree of unsaturation is equal to the number of rings plus the number of pi bonds in a molecule. Ephedrine has one ring and three pi bonds, so its degree of unsaturation is four.
To arrive at this answer, one could also use the formula below, where
For ephedrine,
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Which of the following molecules contains polar, covalent bonds?
I. 
II. 
III. 
IV. 
V. 
Which of the following molecules contains polar, covalent bonds?
I.
II.
III.
IV.
V.
is an ionic compound, while 
is a nonpolar covalent compound. Remember that polarity results from a difference in the electronegativities of the atoms involved in the bond. Too great of a difference will result in an ionic bond; two of the same atoms will have zero difference, resulting in a nonpolar bond.
, 
, and 
contain polar covalent bonds. In the first two, oxygen will carry a slight negative charge, leaving sulfate and phosphorus with slight positive charges. In 
, chlorine will carry a slight negative charge, leaving the carbon slightly positive. In 
and 
, symmetry helps to balance the polar bonds, resulting in an overall nonpolar molecule, even though the individual bonds are nonpolar.
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Which of the following molecules contains the shortest bond between nitrogen and oxygen?
Which of the following molecules contains the shortest bond between nitrogen and oxygen?
This question is testing your ability to draw Lewis dot structures and your knowledge of how resonance effects bond length. The N-O bond with the greatest pi-bond character will be the shortest; thus, we are looking for a double- or triple-bond between nitrogen and oxygen.
Hydroxylamine (
) only contains single bonds, which have the least pi-bond character.
The nitrite and nitrate ions both have a double bond between the nitrogen and oxygen, but also one or more single bonds between these elements. This means that, because of resonance, the N-O bonds in these molecules will be averaged and our average bond order will be somewhere between single and double. Nitrate will have one double bond and two single bonds, for an average bond order of 1.33. Nitrite has one single bond and one double bond, for a bond order of 1.5.
The nitrosyl ion, however, will contain a triple bonds between the nitrogen and oxygen atoms, giving it the greatest pi-bond character. This bond will contain more energy and be shorter than the bonds in the other answer options.
This question is testing your ability to draw Lewis dot structures and your knowledge of how resonance effects bond length. The N-O bond with the greatest pi-bond character will be the shortest; thus, we are looking for a double- or triple-bond between nitrogen and oxygen.
Hydroxylamine (
The nitrite and nitrate ions both have a double bond between the nitrogen and oxygen, but also one or more single bonds between these elements. This means that, because of resonance, the N-O bonds in these molecules will be averaged and our average bond order will be somewhere between single and double. Nitrate will have one double bond and two single bonds, for an average bond order of 1.33. Nitrite has one single bond and one double bond, for a bond order of 1.5.
The nitrosyl ion, however, will contain a triple bonds between the nitrogen and oxygen atoms, giving it the greatest pi-bond character. This bond will contain more energy and be shorter than the bonds in the other answer options.
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Which of the following represents a triple bond?
Which of the following represents a triple bond?
A sigma bond is a single covalent bond, involving an electron pair located between the two bonding atoms. A pi bond occurs when the p orbitals above and below the bonding atoms overlap, or when the p orbitals to the left and right overlap. In any covalent bond, the first bond formed is a sigma bond and any additional bonds must be pi bonds. Initial orbital overlap always comes from the sigma, or s, subshell; subsequent overlap comes from the pi, or p, subshells.
A sigma bond is a single covalent bond, involving an electron pair located between the two bonding atoms. A pi bond occurs when the p orbitals above and below the bonding atoms overlap, or when the p orbitals to the left and right overlap. In any covalent bond, the first bond formed is a sigma bond and any additional bonds must be pi bonds. Initial orbital overlap always comes from the sigma, or s, subshell; subsequent overlap comes from the pi, or p, subshells.
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For the compound shown below, the hybridization for carbon A is __________ and the hybridization for carbon B is __________.
For the compound shown below, the hybridization for carbon A is __________ and the hybridization for carbon B is __________.
Carbon Ais 
hybridized because this carbon is only bonded to two other atoms. Carbon B is bonded to four atoms, and would therefore be 
hybridized.
Keep in mind that a carbon involved in a triple bond will always be 
hybridized, a carbon involved in a double bond will be 
hybridized, and a carbon involved only in single bonds will be 
hybridized.
Carbon Ais
Keep in mind that a carbon involved in a triple bond will always be
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Using the values from the given table, which single bond would be the most polar?
Using the values from the given table, which single bond would be the most polar?
Electronegativity of a chemical bond can be determined by calculating the electronegativity differences of the elements in a chemical bond. For example, using the values in the table given, the electronegativity differences between the bond are given below:
Based on the calculations above, we can see that the 
bond has the highest difference and therefore has the highest electronegativity.
Electronegativity of a chemical bond can be determined by calculating the electronegativity differences of the elements in a chemical bond. For example, using the values in the table given, the electronegativity differences between the bond are given below:
Based on the calculations above, we can see that the
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Which of the following molecules is not capable of hydrogen bonding?
Which of the following molecules is not capable of hydrogen bonding?
A molecule is capable of hydrogen bonding when a hydrogen atom is attached to a nitrogen, oxygen, or fluorine atom in the molecule. Methanal consists of a central carbon bound to two hydrogen atoms and a double bond with an oxygen atom. The hydrogen atoms are bound only to the carbon, and thus cannot form hydrogen bonds.
Hydrofluoric acid, ethanol, and ammonia are all capable of hydrogen bonding.
A molecule is capable of hydrogen bonding when a hydrogen atom is attached to a nitrogen, oxygen, or fluorine atom in the molecule. Methanal consists of a central carbon bound to two hydrogen atoms and a double bond with an oxygen atom. The hydrogen atoms are bound only to the carbon, and thus cannot form hydrogen bonds.
Hydrofluoric acid, ethanol, and ammonia are all capable of hydrogen bonding.
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Which compound exhibits hydrogen bonding?
Which compound exhibits hydrogen bonding?
Hydrogen bonding occurs between a hydrogen atom and an atom that has a high electronegativity such as fluorine, oxygen, or nitrogen. In this case, the only compound that exhibits hydrogen bonding is water, which has a hydrogen bonded to an oxygen atom. Note that in most cases hydrogen bonding is intermolecular, but in some cases, hydrogen bonding can occur intramolecularly.
Hydrogen bonding occurs between a hydrogen atom and an atom that has a high electronegativity such as fluorine, oxygen, or nitrogen. In this case, the only compound that exhibits hydrogen bonding is water, which has a hydrogen bonded to an oxygen atom. Note that in most cases hydrogen bonding is intermolecular, but in some cases, hydrogen bonding can occur intramolecularly.
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Which of the following compounds is not held together by ionic bonds?
Which of the following compounds is not held together by ionic bonds?
Covalent bonds are formed when two nonmetals are bonded together. This covalent bond means that the electrons are shared by the two atoms in order to satisfy each atom's octet. There is very little difference in the electronegativities of the two atoms involved in the bond, so neither atom pulls the electrons closer to its nucleus.
Ionic bonds are formed between a metal and a nonmetal. Due to the dramatic difference between the electronegativities of metals and nonmetals, the electrons are pulled tightly to the nonmetal, and away from the metal nucleus. This results in each atom having a full octet, even though the electrons are not shared.
Carbon and oxygen are both nonmetals, so we would expect only covalent bonds in carbon dioxide.
Covalent bonds are formed when two nonmetals are bonded together. This covalent bond means that the electrons are shared by the two atoms in order to satisfy each atom's octet. There is very little difference in the electronegativities of the two atoms involved in the bond, so neither atom pulls the electrons closer to its nucleus.
Ionic bonds are formed between a metal and a nonmetal. Due to the dramatic difference between the electronegativities of metals and nonmetals, the electrons are pulled tightly to the nonmetal, and away from the metal nucleus. This results in each atom having a full octet, even though the electrons are not shared.
Carbon and oxygen are both nonmetals, so we would expect only covalent bonds in carbon dioxide.
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Given the salt 
, what is the charge on the manganese ion in this molecule?
Given the salt
In order to determine the charge of the transition metal manganese in the molecule, 
, we must first determine the net charge of the molecules it is bonded to. The manganese is bonded to three fluoride ions. Fluoride ion carries a negative one charge. since it is a halogen The subscript in front of the fluoride in the molecule tells us that we have three fluoride ions. Each fluoride ion carries a 
charge and because we have 3 of them, there is a total charge of 
from these fluoride ions. Molecules like to exist in their most stable state which gives them an overall charge of zero. Therefore, the manganese atom will carry a charge of 
to counter the 
charge from the three fluoride ions.
In order to determine the charge of the transition metal manganese in the molecule,
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Which of the following solids is most ionic?
Which of the following solids is most ionic?
An ionic bond is a bond that occurs between a metal and a nonmetal, which may dissociate into two ions of opposite charges (positive and negative). These bonds are formed by electrostatic forces. We can determine if a compound is ionic from what it is composed of. Ionic compounds can easily be identified because they are generally composed of a metal and non-metal such as 
. Metals are cations and non-metals are anions. In the options given, the substance that contains an ionic bond is 
. The ions involved are 
and 
.
An ionic bond is a bond that occurs between a metal and a nonmetal, which may dissociate into two ions of opposite charges (positive and negative). These bonds are formed by electrostatic forces. We can determine if a compound is ionic from what it is composed of. Ionic compounds can easily be identified because they are generally composed of a metal and non-metal such as
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Given the salt 
, what is the charge on the barium ion in this molecule?
Given the salt
In order to determine the charge of the barium ion in the molecule, 
, we must first determine the net charge of the molecules it is bonded to. The barium ion is bonded to two fluoride ions.
Fluoride ion carries a -1 charge. The subscript in front of the fluoride in the molecule tells us that we have two fluoride ions. Each fluoride ion carries a -1 charge and because we have 2 of them, there is a total charge of -2 from these fluoride ions. Molecules like to exist in their most stable state which gives them an overall charge of zero. Therefore, the barium atom will carry a charge of +2 to counter the -2 charge from the two fluoride ions.
In order to determine the charge of the barium ion in the molecule,
Fluoride ion carries a -1 charge. The subscript in front of the fluoride in the molecule tells us that we have two fluoride ions. Each fluoride ion carries a -1 charge and because we have 2 of them, there is a total charge of -2 from these fluoride ions. Molecules like to exist in their most stable state which gives them an overall charge of zero. Therefore, the barium atom will carry a charge of +2 to counter the -2 charge from the two fluoride ions.
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Given the salt 
, what is the charge on the 
ion in this molecule?
Given the salt
In order to determine the charge of the 
ion in the molecule, 
, we must first determine the net charge of the molecules it is bonded to. The 
ion is bonded to a 
ions.
ion is one a common anion and carries a -2 charge. Molecules like to exist in their most stable state which gives them an overall charge of zero. 
has an overall charge of zero. Therefore, the 
atom will carry a charge of +2 to counter the -2 charge from the 
ion.
In order to determine the charge of the
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Which answer option correctly depicts the Lewis dot structure of sodium chloride?
Which answer option correctly depicts the Lewis dot structure of sodium chloride?
When drawing a Lewis dot structure, we are always trying to reach an electron count where all atoms involved are stable and (usually) have full octets. We are also trying to estabilsh a structure in which we have the smallest formal charge possible. The general rule is first to draw out all of the elements involved and their valence electrons, then start piecing them together trying to reduce the formal charge and get all elements involved to an octet. There are a couple exceptions to the octet rule.
Sodium and chlorine form an ionic bond, meaning that one atom will donate an electron and the other will receive it. This gives each atom a charge. Chlorine has seven valence electrons, while sodium has one valence electron. For each atom to arrive at an octet, sodium will need to lose one electron and chlorine will need to gain one electron. This would give chlorine a negative charge, and sodium a positive charge.
Thus, the answer is a sodium with a positive charge (due to one lost electron) and a chlorine with eight electrons and a negative charge (due to one electron gained).
When drawing a Lewis dot structure, we are always trying to reach an electron count where all atoms involved are stable and (usually) have full octets. We are also trying to estabilsh a structure in which we have the smallest formal charge possible. The general rule is first to draw out all of the elements involved and their valence electrons, then start piecing them together trying to reduce the formal charge and get all elements involved to an octet. There are a couple exceptions to the octet rule.
Sodium and chlorine form an ionic bond, meaning that one atom will donate an electron and the other will receive it. This gives each atom a charge. Chlorine has seven valence electrons, while sodium has one valence electron. For each atom to arrive at an octet, sodium will need to lose one electron and chlorine will need to gain one electron. This would give chlorine a negative charge, and sodium a positive charge.
Thus, the answer is a sodium with a positive charge (due to one lost electron) and a chlorine with eight electrons and a negative charge (due to one electron gained).
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What is the Lewis dot structure for 
?
What is the Lewis dot structure for
When drawing a Lewis dot structure, we are always trying to reach an electron count where all atoms involved are stable and (usually) have full octets. We are also trying to estabilsh a structure in which we have the smallest formal charge possible. The general rule is first to draw out all of the elements involved and their valence electrons, then start piecing them together trying to reduce the formal charge and get all elements involved to an octet. There are a couple exceptions to the octet rule.
In this case, boron actually has an incomplete octet. Though there are resonance forms in which boron has a full octet, when you calculate the formal charge of these configurations it will not be zero.
When drawing a Lewis dot structure, we are always trying to reach an electron count where all atoms involved are stable and (usually) have full octets. We are also trying to estabilsh a structure in which we have the smallest formal charge possible. The general rule is first to draw out all of the elements involved and their valence electrons, then start piecing them together trying to reduce the formal charge and get all elements involved to an octet. There are a couple exceptions to the octet rule.
In this case, boron actually has an incomplete octet. Though there are resonance forms in which boron has a full octet, when you calculate the formal charge of these configurations it will not be zero.
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What is the molecular shape of 
?
What is the molecular shape of
NH3 is trigonal pyramidal because it has 4 electron domains, one of them being a lone pair of electrons and the other three being H atoms. When this is arranged in a three-dimensional space, it is trigonal pyramidal in shape.
NH3 is trigonal pyramidal because it has 4 electron domains, one of them being a lone pair of electrons and the other three being H atoms. When this is arranged in a three-dimensional space, it is trigonal pyramidal in shape.
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Which of the following is not the correct geometric configuration for the given molecule?
Which of the following is not the correct geometric configuration for the given molecule?
Recall the following relationships between geometry and number of pairs of electrons on the central atom.
2: linear
3: trigonal planar
4: tetrahedral
5: trigonal bipyriamidal
6: octahedral
To visualize the geometry, we need to think of how many electron pairs are on the central atom. Drawing Lewis dot diagrams may be helpful here. None of the answer choices has lone central electron pairs, with the exception of water, so the number of atoms bound to the central atom is the same as the number of central electron pairs.
The only one that does not match up with the correct geometry is SF6, which is actually octahedral since it has six central electron pairs. In a water molecule, the central oxygen has six valence electrons, plus one from each bond with hydrogen, for a total of eight central electrons and four central electron pairs. So, this geometry is a variation on the tetrahedral form (bent), in which two central electron pairs are not bound.
Recall the following relationships between geometry and number of pairs of electrons on the central atom.
2: linear
3: trigonal planar
4: tetrahedral
5: trigonal bipyriamidal
6: octahedral
To visualize the geometry, we need to think of how many electron pairs are on the central atom. Drawing Lewis dot diagrams may be helpful here. None of the answer choices has lone central electron pairs, with the exception of water, so the number of atoms bound to the central atom is the same as the number of central electron pairs.
The only one that does not match up with the correct geometry is SF6, which is actually octahedral since it has six central electron pairs. In a water molecule, the central oxygen has six valence electrons, plus one from each bond with hydrogen, for a total of eight central electrons and four central electron pairs. So, this geometry is a variation on the tetrahedral form (bent), in which two central electron pairs are not bound.
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Which of the following molecules exhibits a trigonal pyramidal geometry?
Which of the following molecules exhibits a trigonal pyramidal geometry?
The trigonal pyramidal geometry is implemented by molecules in which the central atom has three atoms and a lone pair attached. 
has three hydrogens attached to the central phosphorus as well as a lone pair, which can be determined by drawing the Lewis structure of the molecule. As a result, it has trigonal pyramidal geometry.
is trigonal planar. 
is tetrahedral. 
is octahedral.
The trigonal pyramidal geometry is implemented by molecules in which the central atom has three atoms and a lone pair attached.
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