Physical Chemistry Third Edition

914 21 The Electronic Structure of Polyatomic Molecules

21.88Using one of the available computational chemistry
programs, carry out a semiempirical or ab initio
calculation for
a.NH 3
b.BH 3
c.The adduct of NH 3 and CH 3
Compare your results with those of the previous problem.

21.89Identify each statement as either true or false. If a
statement is true only under special circumstances, label
it as false.
a.Hybrid orbitals are used to allow reasonable
approximate molecular orbitals to be written as linear
combinations of only two atomic orbitals.
b.Every orbital must be an eigenfunction of every
operator that belongs to the molecule.
c.If the self-consistent field method were
carried out to exact consistency, correct wave

functions and correct energy eigenvalues would be

obtained.

d.Configuration interaction is one way to reduce the

correlation error.

e.In a variation wave function, introducing explicit

dependence on electron–electron distances is one way

to reduce the correlation error.

f.The symmetry operators that belong to any object form

a mathematical group.

g.Only abelian groups can correspond to molecules in

their equilibrium conformations.

h.Thesphybrid orbitals can be used only with linear

molecules.

i.Thesp^2 hybrid orbitals can be used only with trigonal

planar molecules.

j.The Hückel method is used only for planar molecules

with delocalized orbitals.