Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
78 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 8
Sometimes there are exceptions to the octet rule. There may be
an odd number of total valence electrons, as in the case of ClO 2 .
Alternatively, a central atom may have more or fewer than eight
electrons. In the latter case, an atom with a lone pair may attach to it
by means of a coordinate covalent bond, a bond in which both
shared electrons are donated by only one of the atoms.
Practice Problems
10. Draw the three resonance structures for the carbonate ion
(CO 3
2Ϫ ). (Hint: Each structure contains one double bond.)
11. State why each of the following is an exception to the octet
rule.
a. NO 2
b. BCl 3
c. PF 5
8.4 Molecular Shape
The VSEPR model is used to determine molecular shape. It
assumes arrangements that minimize repulsion of electron pairs
around the central atom. The presence of four bonding pairs produces a tetrahedral arrangement. Three such pairs produce a trigonal
planar shape, unless there also is a lone pair on the central atom, in
which case the shape is trigonal pyramidal. Two bonding pairs produce a linear shape, but if there also are two lone pairs on the central
atom, the shape will be bent.
During bonding, atomic orbitals can undergo hybridization, or
mixing to form new, identical hybrid orbitals. An s orbital and three
p orbitals can hybridize to form four identical sp 3 hybrid orbitals.
That produces a tetrahedral, trigonal pyramidal, or bent molecular
shape, depending on whether none, one, or two of these orbitals contain lone pairs (as in the case of CH 4 , NH 3 , and H 2 O, respectively).
The hybridization of an s and two p orbitals produces three sp 2
hybrid orbitals, which produces a trigonal planar shape (as in the
case of AlCl 3 ). The hybridization of an s and one p orbital produces
two sp hybrid orbitals, which produce a linear shape (as in the case
of BeCl 2 ).
78 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 8
Sometimes there are exceptions to the octet rule. There may be
an odd number of total valence electrons, as in the case of ClO 2 .
Alternatively, a central atom may have more or fewer than eight
electrons. In the latter case, an atom with a lone pair may attach to it
by means of a coordinate covalent bond, a bond in which both
shared electrons are donated by only one of the atoms.
Practice Problems
10. Draw the three resonance structures for the carbonate ion
(CO 3
2Ϫ ). (Hint: Each structure contains one double bond.)
11. State why each of the following is an exception to the octet
rule.
a. NO 2
b. BCl 3
c. PF 5
8.4 Molecular Shape
The VSEPR model is used to determine molecular shape. It
assumes arrangements that minimize repulsion of electron pairs
around the central atom. The presence of four bonding pairs produces a tetrahedral arrangement. Three such pairs produce a trigonal
planar shape, unless there also is a lone pair on the central atom, in
which case the shape is trigonal pyramidal. Two bonding pairs produce a linear shape, but if there also are two lone pairs on the central
atom, the shape will be bent.
During bonding, atomic orbitals can undergo hybridization, or
mixing to form new, identical hybrid orbitals. An s orbital and three
p orbitals can hybridize to form four identical sp 3 hybrid orbitals.
That produces a tetrahedral, trigonal pyramidal, or bent molecular
shape, depending on whether none, one, or two of these orbitals contain lone pairs (as in the case of CH 4 , NH 3 , and H 2 O, respectively).
The hybridization of an s and two p orbitals produces three sp 2
hybrid orbitals, which produces a trigonal planar shape (as in the
case of AlCl 3 ). The hybridization of an s and one p orbital produces
two sp hybrid orbitals, which produce a linear shape (as in the case
of BeCl 2 ).