COVALENT BONDING
31
½ s
½ p
s p
+
two sp orbitals in
linear array
side view:
two sp hybrid orbitals
+ two p orbitals
180˚
end view:
two p orbitals
Figure 2.18 sp hybrid orbitals
π bonds
π bonds
formation of one
and
two
σ bonds, plus two
π bonds in acetylene
for clarity, overlap of p
orbitals is represented
by the dotted lines
H
C
H
π molecular orbitals
in acetylene
C C
C H
C C
Figure 2.19 Bonding in acetylene
Hybridization and bond lengths
We also note that there are significant differences in
bond lengths for single, double, and triple bonds. The
carbon atoms in ethane are further apart (1.54 ˚
A) than
in ethylene (1.34 ˚
A), and those in acetylene are even
closer together (1.20 ˚
A); ˚
A refers to the ˚
Angstr¨ om
unit, 10
−10 m. This is primarily a consequence of
the different nature of the σ bonds joining the two
carbons. Because sp
2 hybrid orbitals have less p
character than sp
3 hybrid orbitals, they are less
elongated; consequently, a σ bond formed from sp
2
orbitals will be rather shorter than one involving sp
3
orbitals. By similar reasoning, sp hybrid orbitals will
be shorter than sp
2 orbitals, because they have even
less p character, and will form even shorter C–C
σ bonds.
C
C
H
H
H
H
H
H
C
C
H
H
H
H
C
C
H
H
ethane
ethylene
acetylene
sp
3 sp 3
sp 2 sp 2
sp sp
1.54 Å
1.34 Å
1.20 Å
1.10 Å
1.09 Å
1.08 Å
C
H
H
H
H
depiction of tetrahedral array
using wedged and dotted bonds
a wedged bond indicates it comes
in front of the plane of the paper
a dotted bond indicates it goes
behind the plane of the paper
these bonds are in the
plane of the paper
hybridization
in C−C bond:
31
½ s
½ p
s p
+
two sp orbitals in
linear array
side view:
two sp hybrid orbitals
+ two p orbitals
180˚
end view:
two p orbitals
Figure 2.18 sp hybrid orbitals
π bonds
π bonds
formation of one
and
two
σ bonds, plus two
π bonds in acetylene
for clarity, overlap of p
orbitals is represented
by the dotted lines
H
C
H
π molecular orbitals
in acetylene
C C
C H
C C
Figure 2.19 Bonding in acetylene
Hybridization and bond lengths
We also note that there are significant differences in
bond lengths for single, double, and triple bonds. The
carbon atoms in ethane are further apart (1.54 ˚
A) than
in ethylene (1.34 ˚
A), and those in acetylene are even
closer together (1.20 ˚
A); ˚
A refers to the ˚
Angstr¨ om
unit, 10
−10 m. This is primarily a consequence of
the different nature of the σ bonds joining the two
carbons. Because sp
2 hybrid orbitals have less p
character than sp
3 hybrid orbitals, they are less
elongated; consequently, a σ bond formed from sp
2
orbitals will be rather shorter than one involving sp
3
orbitals. By similar reasoning, sp hybrid orbitals will
be shorter than sp
2 orbitals, because they have even
less p character, and will form even shorter C–C
σ bonds.
C
C
H
H
H
H
H
H
C
C
H
H
H
H
C
C
H
H
ethane
ethylene
acetylene
sp
3 sp 3
sp 2 sp 2
sp sp
1.54 Å
1.34 Å
1.20 Å
1.10 Å
1.09 Å
1.08 Å
C
H
H
H
H
depiction of tetrahedral array
using wedged and dotted bonds
a wedged bond indicates it comes
in front of the plane of the paper
a dotted bond indicates it goes
behind the plane of the paper
these bonds are in the
plane of the paper
hybridization
in C−C bond: