In order to solve the wave equation for the hydrogen atom, it is necessary to transform the Laplacian
into polar coordinates. That transformation allows the distance of the electron from the nucleus to
be expressed in terms of r , θ , and φ , which in turn allows the separation of variables technique to be
used. Examination of Eq. (2.40) shows that the fi rst and third terms in the Hamiltonian are exactly
like the two terms in the operator for the hydrogen atom. Likewise, the second and fourth terms are
also equivalent to those for a hydrogen atom. However, the last term, e
2 / r 12 , is the troublesome part of
the Hamiltonian. In fact, even after polar coordinates are employed, that term prevents the separation
of variables from being accomplished. Not being able to separate the variables to obtain three simpler
equations prevents an exact solution of Eq. (2.40) from being carried out.