if i am to calculate the energy of an electron in the 3d orbital of oxygen atom.....how i am supposed to consider the electronic configuration? i mean i can easily do so for 2p or 2s using slaters rule....because the electrons are present in those orbitals but for the 3d case where should i consider the electron to be present? i mean i dont know if there are any electrons above 3d or not. i know the value of R(h) and (n) but cant calculate the effective nuclear charge. formula = R(h)*z^2/n^2 also how should i calculate the most probable radius? so how do i proceed?