1. Noble Gases Argon :1s2 2s2 2p6 3s2 3p6
Potassium: 1s2 2s2 2p6 3s2 3p6 4s1
Simplified electron configuration for Argon: [Ar]
Simplified electron configuration for Potassium: [Ar] 4s1
Noble Gas Simplification

2. Noble Gas Simplification
Take the last noble gas before the element of interest
Put the noble noble gas we put into the brackets
Finish the electron configuration for the element
Example:
Aluminum: [Ne]3s23p1 
Calcium: [Ar]4s2

3. Noble Gas Simplification
This notation for writing electron configurations helps us to highlight 2 different types of electrons in the atom
1. Electrons in the brackets are called core electrons
These electrons do not participate in chemical reactions
2. The electrons written after the [noble gas] are called valence electrons
Valence electrons are those electrons in the highest principal energy level
These electrons are important because they are the ones that are gained, lost or shared in chemical reactions.

4. Noble Gas Simplification
Aluminum: [Ne]3s23p1 
This tells us that there are 2 electrons in the 3s orbital and 1 electron in the 3p orbital so aluminum has a total of 3 valence electrons
Calcium: [Ar]4s2
valance electrons: 2
Manganese: [Ar]4s23d5
Valance electrons: 2
Iodine: [Kr]:5s24d105p5
Valence electrons: 7

5. Electron Configurations
Atoms
Al: 1s2 2s2 2p6 3s2 3p1
Ions
Al-
Gained an electron
1s2 2s2 2p6 3s2 3p2
Al+
Lost an electron
1s2 2s2 2p6 3s2
Al3+
Lost 3 electrons
1s2s2p6
Work sheets:
Valence Electrons
Noble Gases