1. KEY
GENERAL CHEMISTRY-I (1411)
S.I. # 33
1. a) What are the similarities and differences between atomic orbitals and
molecular orbitals? b) Why is the bonding molecular orbital of H2 at lower energy
than the electron in a hydrogen atom? c) How many electrons can be placed into
each MO of a molecule?
a) both have a region where there is high probability of finding an electron. Each
atomic orbital or molecular orbital can hold a max of two electrons. Atomic orbitals are
localized on a single atom and their energies are the result of interactions between the
subatomic particles in a single atom. MOs can be delocalized over several or even all the
atoms in a molecule and their energies are influenced by interactions between electrons
on several atoms.
b) There is a net stabilization (lowering in energy) that accompanies bond
formation because the bonding electrons in H2 are strongly attracted to both H nuclei
c) Two
2. a) what are the relationships among bond order, bond length, and bond energy?
b) According to molecular orbital theory, would either Be2 or Be2+ be expected to
exist? Explain.
a) When comparing the same two bonded atoms, the greater the bond order, the
shorter the bond length and the greater the bond energy. That means the bond order and
the bond energy are directly related, while bond order and bond length are inversely
related. When comparing different bonded nuclei, there are no simple relationships.
b) Be2, 4e- ↑↓ Bond order = (1/2) (2-2) = 0
σ*2s
↑↓
σ2s
Be2+, 3e ↑_ Bond order = (1/2)(2-1) = 0.5
σ*2s
↑↓
σ2s
Be2 has a bond order of zero and is not energetically favored over isolated Be atoms; it is
not expected to exist. Be2+ has a bond order of 0.5 and is slightly lower in energy than
isolated Be atoms. It will probably exist under special experimental conditions but be
unstable.

2. KEY
The remainder of this sheet is blank for any last questions on the new material from
chapters 7-9.