To illustrate the use of the foregoing rules, we will write the Slater wave function for an electron in
an oxygen atom. The electron resides in a 2 p orbital, so n 2, which means that n * 2. There are
four electrons in the 2 p orbitals in an oxygen atom, so the fourth electron is screened by three others.
However, an electron in a 2 p orbital is also screened by the two electrons in the 1 s orbital and two in
the 2 s orbital. Two electrons in the 1 s level give screening that can be written as 2(0.85) 1.70. The
screening constant is the same for electrons in the 2 s and 2 p states, and the electron in the 2 p state that
is being considered has fi ve other electrons involved in screening. Therefore, those fi ve give a contribution to the screening constant of 5(0.35) 1.75. Adding the contributions gives a total screening constant of 1.70 1.75 3.45, which means that the effective nuclear charge is 8 3.45 4.55. Using
this value gives ( Z s )/ n * 2.28 and a Slater wave function that can be written as