Covalent Bonding - 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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