Understanding shells and subshells helps us see how electrons are organized in an atom.

You can think of shells like layers of an onion. Each layer can hold a certain number of electrons.

Shells:

• The first shell (n=1) holds up to 2 electrons.
• The second shell (n=2) can hold up to 8 electrons.
• The third shell (n=3) can hold up to 18 electrons.

Subshells: Inside each shell, there are smaller parts called subshells. Think of these like rooms in a layer.

• The s subshell holds 2 electrons.
• The p subshell holds 6 electrons.
• The d subshell holds 10 electrons.
• The f subshell holds 14 electrons.

Here’s a simple example: the electron configuration for carbon, which has 6 electrons, is written as $1s^2 2s^2 2p^2$.

This means that carbon has 2 electrons in the first shell (1s) and 4 electrons in the second shell (2s + 2p).

So, shells and subshells help us understand where electrons are in an atom!