Writing electron configuration for different elements is quite simple with the use of a periodic table. Simply split the periodic table into s,p,d and f blocks and use the period # to determine the energy level (d 1 behind, f 2 behind) Exceptions to this do occur for Cr, Cu and many others in the transition metals. Ions have additional electrons or missing electrons IE F 1s2 2s2 2p5 and F- is 1s2 2s2 2p6 Na is 1s2 2s2 2p6 3s1 and Na+ is 1s2 2s2 2p6 An electron configuration is a simple description where labels are applied to each electron in an element that later can be used to discuss why electrons exhibit specific behaviors in ionization energies, chemical reactions and bonding. The rules for why electron configurations are what they are come from quantum mechanics and some basic information about quantum numbers and the rules such as Hund's rule, Pauli's exclusion principle and the Aufbau principle are discussed.