Answers and Explanations
REVIEW QUESTIONS
1 . sp: the carbon forms a single bond and a triple bond.
2 . sp: the carbon forms a single bond and a triple bond.
3 . sp^3 : the carbon forms four single bonds.
4 . sp^2 : the carbon forms a double and two single bonds.
5 . There are eight single bonds, one double bond, and one triple bond. Each single bond gives a σ
bond; a double bond gives one σ and one π bond; a triple bond gives one σ and two π bonds.
So there is a total of 8 + 1 + 1 = 10 σ bonds, and 1 (from double bond) + 2 (from triple bond) = 3
π bonds in the molecule.
6 . A
The two carbon atoms in ethene are bonded to each other via a double bond. They are thus
both sp^2 hybridized and the three attached groups each has will be arranged in a planar
configuration roughly 120° apart, since that will minimize the electron-pair repulsion. Choice B
is wrong because of the bond angle. The other choices are wrong because both carbons are sp^2
hybridized; sp hybridization is found on carbon atoms with two adjacent double bonds
(allenes) or, more commonly, a triple bond and a single bond (alkynes), while sp^3 hybridization
is found on saturated carbon atoms.
7 . C
A saturated hydrocarbon is one that contains only single bonds. If it is noncyclic, its formula
will conform to that of alkanes: CnH 2 n (^) + 2 . Only choice C satisfies this.
8 . D