CHEM 109A
CLAS
Drawing 3-D Orbital Structures/Diagrams - KEY
1. Draw 3-D orbital structures for each of the following.
a. Water
sp3
O
H
O
H
H
H
s
H2O
b. Ammonia
H
H
N sp3
N
H
H
H
H
NH3
c. Methyl cation
+
CH3
H
H
sp2
+
C
H
H
+
C
H
H
empty, unhybridized p orbital
d. Methyl anion
CH3
H
lone pair in sp3 orbital
3
sp
-
C
H
H
H
H
H
e. Ethene
C2H4
Page 1 of 5
CHEM 109A
CLAS
Drawing 3-D Orbital Structures/Diagrams - KEY
unhybridized p orbitals on Cs
overlap above and below
plane of molecule to form π
bond
H
H
H
H
H
both Cs sp2
H
H
H
σ + π = double bond
f. Carbon dioxide
CO2
lone pairs in sp2 orbitals
sp
O
O
O
sp2
O
2 π bonds perpendicular to
each other, due to overlap of
unhybridized
p
orbitals
between C and each O.
g. Nitric acid
HNO3
sp2
sp3
O
O
+
O
-
+
sp2 in both
N
H
N
-
O
O
sp3
both resonance structures
O
sp3 in both
sp2
1
H
will draw all atoms sp2 to satisfy
2
O
O
O
-
N
O
+
-
N
+
H
H
O
O
1
2
h. Formic acid
Page 2 of 5
CHEM 109A
CLAS
Drawing 3-D Orbital Structures/Diagrams - KEY
HCOOH
O
O
H
H
-
H
O
C sp2 in both
O
sp3
+
H
sp2
1
2
O
O
H
H
H
H
O
O
1
+
2
i. Hydrocyanic acid
HCN
H
N
H
sp
lone pair in sp orbital
N
σ + 2 π bonds = triple bond
j. HCNO (noncyclic and connected as shown)
Best resonance structures*
+
H
N
sp
H
O
3
sp
sp
N
O
+
H
-
-
sp
H
+
C
2
N
O
sp
sp2
N
O
+
-
lone pairs in sp2 orbitals and
unhybridized p orbital on O
Page 3 of 5
CHEM 109A
CLAS
Drawing 3-D Orbital Structures/Diagrams - KEY
*It would actually be best to show the O as being sp hybridized so that a pi bond
could be formed in the y-plane as well as the z-plane in which case only one lone pair
would be in an sp hybrid orbital and the other two would be in unhybridized p orbitals.
k. Also try hydronium ion, CH3CH2NH- and CH2CN-, nitrite ion
l. Tougher ones: ethyl radical, propene, acetylene
Additional Information:
3-D orbital structures/diagrams are used to show the orbitals & e- occupancies for
atoms in more detail than Lewis-Kekule structures. BE DETAILED!
Steps for Drawing 3-D Orbital Structure:
1. Draw Lewis-Kekule structure.
a. Include resonance structures where appropriate
2. Determine hybridization on EACH atom
For atoms in the second period of the PT, we have the following orbitals
s
px
to mix/hybridize
Mix
Hybridization
s and px
sp
pz
Hybrid orbital
(# of them)
(2)
║to paper
py
Bond angles
Geometry
180o
Linear
120o
Trigonal
Planar
s and px and py
sp2
(3)
┴ to paper
s and px and pz
(3)
Page 4 of 5
CHEM 109A
CLAS
Drawing 3-D Orbital Structures/Diagrams - KEY
s and px , py and pz
sp3
109.5o *
Tetrahedral
(4)
*Notable exceptions that will be assumed to be tetrahedral
water w/ bond angle ~104o
ammonia w/ bond angle ~107o
a. hybridization on an atom must be the same in all resonance structures, so chose
least hybridized. For example, if an O is sp2 hybridized in one resonance structure and
sp3 hybridized in another, you should draw it as being sp2 hybridized in both.
3. Starting with the more central atom draw the 3-D orbital diagram
a. Single lines represent sigma bonds and can be solid (in plane of paper),
dashed (away from you, into paper) or wedged (towards you, out of
paper).
b. Include unhybridized orbitals (usu. p orbitals) on each atom since is it
overlap of these orbitals that creates pi bonds.
c. Place lone pairs as paired up and down arrows in orbitals (usu. hybridized,
but sometimes unhybridized p orbitals).
4. Count up number of e-s – should equal the number of e-s in your Lewis-Kekule
structure (#1).
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