Question

    

    

Write the ground state electron configuration of Ca using the noble-gas shorthand notation.

Answer 1

[Ar] 4s2

Answer 2

Noble Gas Simplification

Now, this is becoming a lot of work writing down these ever-expanding electron configurations!  The more electrons we have in the atom, the longer the electron configuration.  We have a method we can use to simplify writing these configuration as we become more familiar with them.   If we look closely, we notice that the electron configuration for rubidium is the same as the previous element, argon, with a single 5s electron added on.  For the electron configuration of argon, let us simply write [Kr].  The simplified electron configuration for rubidium then becomes:

Rubidium

[Kr]5s1

We can do this for any element, BUT, we must use only noble gases in the brackets.  I call this the noble gas simplification.  In this method of writing electron configurations, the last noble gas before we get to the element of interest is the noble gas we put into the brackets.  For instance, for the element aluminum we write

Sulfur	[Ne]3s23p4
Chlorine	[Ne]3s23p5
Argon	[Ne]3s23p6
Potassium	[Ar]4s1
Calcium	[Ar]4s2

We may NOT use any element in the brackets, only noble gases.

Valence Electrons-This notation for writing electron configurations helps us to highlight 2 different types of electrons in the atom.  Those electrons in the brackets are called core electrons.  These electrons do not participate in chemical reactions.   The electrons written after the noble gas in brackets are called valence electrons.   In many cases,