Solutions to Homework
October 20
14.24. Bonding MOs have most of their electron density in-between the nuclei they are bonding. Anti-bonding MOs have most of their electron density NOT in-between the nuclei they are bonding. To understand what is meant by 'in-between', imagine that the two nuclei being bonded are each on a plane, the two planes are parallel to each other. If most of the orbital's density is in between these two parallel planes, then the MO is a bonding MO. If most of the orbital's density is outside these two parallel planes, then the MO is an anti-bonding MO.
14.26. a. All four of these would have the same MO diagram;
composed of two orbitals, a s (lower energy than the
1s atomic orbitals of the H atom) and a s* (higher
energy than the 1s atomic orbitals of the H atom). The four species listed
each have one more electron than the one before them. H2+
puts one electron in the s bond for a bond order of
1/2. stable
H2 puts two electrons in the s bond for a
bond order of 1. Stable
H2- puts two electrons in the s
bond and one electron in the s* for a bond order of
1/2. Predicted to be stable (but doesn't exist)
H22- puts two electrons in the s
bond and two electrons in the s* for a bond order of
0. Not stable.
b. All three of these will have the same MO
diagram composed of two orbitals, a s (lower
energy than the 1s atomic orbitals of the H atom) and a s*
(higher energy than the 1s atomic orbitals of the H atom).
He22+ puts two electrons in the
s bond for a bond order of 1. Stable
He2+ puts two electrons in the s
bond and one electron in the s* for a bond order of
1/2. stable
He2 puts two electrons in the s bond
and two electrons in the s* for a bond order of 0.
Not stable.
c. Read section 14.3
14.28. See the picture posted on the bulletin board outside my office, or Figure 14.36..
.