Electron Energy Sublevels:

The shape of the Periodic Table makes the four sublevels easy to see.

• s sublevel - the two tall columns on the left.

  Helium is at the far right because it is inert (like the other Nobel Gases). For the purpose of reading sublevels, it should be thought of as sitting in the second column beside hydrogen.

• p sublevel - the six tall columns on the right, without helium.
   
• d sublevel - the ten short columns in the middle of the table.
   
• f sublevel - the fourteen columns of two below the main body of the table.

The sublevel areas on the Periodic Table are referred to as "blocks".

• s-block
• p-block
• d-block
• f-block
• g-block (on the extended periodic table)

The Periodic Table does not show the overlap of the d and f sublevels. Both of these sublevels overlap the s sublevel of the next lowest electron energy level.

• Even though the first elements in the d sublevel on the Periodic Table are on the fourth row, the first electron energy level to have a d sublevel is the 3^rd energy level.
   
• Even though the first elements in the f sublevel on the Periodic Table are on the fifth row, the first electron energy level to have an f sublevel is the 4^th energy level.
   
• These energy overlaps will be explained in the next concept.