Electron filling shell formula?

Question

i want some formula which help me to find the correct order of filling shell of some specific atom . for example Gd=64

Answer 1

I hope this will help you. :-)
http://upload.wikimedia.org/wikipedia/commons/1/11/Electron_orbitals.svg
or
http://en.wikipedia.org/wiki/Image:Electron_orbitals.svg

Answer 2

You know that the electron shells and subshells are filled in the increasing order of shells and after subshells.

ex you fill first 1s , after 2s, 2p after 3s, 3p and after you should fill 3d but here there is an eception you fill 4s and after 3d . So a rule cannot be given for atoms with Z>18

You find the electron configuration in a periodic table

for Gd 1s2, 2s2, 2p6, 3s2, 3p6,4s2, 3d10, 4p6,5s2 ,4d10,5p6,6s2, 4f7,5d1