Electron configurations can be read directly from the periodic table.

• Helium must be moved into the s-block next to hydrogen, (because its 2 electrons are in the 1s orbital).
   
• Each square on the table represents an electron.
   
• The shape of the table identifies the subshells (the s, p, d, and f blocks) and each horizontal row represents a given value for n.

The square representing sodium has been darkened on the table above. Click on the table to see how counting the squares will give sodium's electron configuration.

There are two ways to check any electron configuration: 1s22s22p63s1

1. The last notation in the electron configuration represents the location of the element on the periodic table.

   The 3s¹ in sodium's electron configuration identifies its location on the Periodic Table as:

   • third energy level
   • s sublevel
   • first box

2. The total of the superscripts in an electron configuration equals the atomic number of the element.

   The total of the superscripts in sodium's electron configuration is 11, its atomic number.

 
Electron configuration

 
Electron configuration