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