Core Notation

So by this point, we all know how to do electron configuration.

Core Notation is basically just simplifying core notation!

The set of electrons for an atom can be divided into two subsets: core and outer.

The CORE of an atom is the set of electrons with the configuration of the nearest noble gas (He, Ne, Ar, Kr, etc.) that comes before it.

The OUTER electrons consist of all electrons outside the core. These normally take part in chemical reactions.

So, how do you do this "core notation"? 

At first, it made absolutely no sense to me at all.

But as I continued practicing, I found out it's actually pretty simple.

Step 1: Locate the atom and note the noble gas at the end of the row ABOVE the element.

As you can (hopefully) see in this picture of the periodic table, I've highlighted the noble gases that can be used in Core Notation.

For example - Chlorine.

The Electron configuration for Chlorine is 1s² 2s² 2p⁶ 3s² 3p⁵

Okay, so what is the noble gas at the end of the row above the element? Locate Chlorine. You will see that at the end, and up one, is Neon. 

The Electron Configuration for Neon is 1s² 2s² 2p⁶

STEP 2: Replace the part of the configuration corresponding to the configuration of the noble gas, with the SYMBOL for the NOBLE GAS in SQUARE BRACKETS. 

So in this case, the CORE NOTATION of Chlorine would be: 

It's simple! This way, you don't have to keep writing out 1s² 2s² 2p⁶ etc.