High School Physics

# Electron shells for the first 20 elements & shells filling rules

In this post, we will present a diagram displaying the electron shells for the first 20 elements of the Periodic Table.
The number of electrons increases by 1 each time. (It is the same as the proton number.)

The shells fill according to the rules given in the next section.

## Electron shells filling rules

Electrons are arranged in shells around the nucleus.

The first shell, closest to the nucleus, is the lowest energy level. The further a shell is from the nucleus, the higher the energy level.
Each shell can hold only a certain number of electrons.

These are the rules ( Electron shells filling rules )

• The first shell can hold only 2 electrons. It fills first.
• The second shell can hold 8 electrons. It fills next.
• The third shell can hold 18 electrons. But it fills up to 8. The next 2 go into the fourth shell. Then the rest of the third shell fills.

## Electron shells for the first 20 elements

The following diagram displays the electron shells for the first 20 elements of the Periodic Table.