Some more examples of electron structures are given here.

The short hand method using the core electrons, defined as all electrons up to and including those involved in the last noble gas (He, Ne, Ar, Kr, Xe or Rn) encountered, one may desigate all these electrons as the core designation in brackets, example [Ar], and then continue with the rest of the configuration.  

Example:  for arsnic, As:

    electron configuratoin = [Ar] 4s²3d¹⁰ 4p²

The other electrons are called valence electrons.  (4s² 3d¹⁰4p² in the above example)

Note:  if you end up with the noble gas structure  and you are using the short hand method, back up to the previous noble gas as the core.