where a 0 , the fi rst Bohr radius, is 0.529 Å. The expectation value for the radius of the 1 s orbit is 1.5
times that distance. Note that a complicated-looking problem actually turns out to be much simpler
than might have been supposed. In this case, looking up two integrals in a table removes the neces-
sity for integrating the functions by brute force. A great deal of elementary quantum mechanics can be
handled in this way.