Here's why:

* Atomic Number: Chlorine has an atomic number of 17, meaning it has 17 protons and 17 electrons.

* Electron Configuration: The electron configuration of chlorine is 2, 8, 7. This means:

* The first shell (n=1) holds 2 electrons.

* The second shell (n=2) holds 8 electrons.

* The third shell (n=3) holds 7 electrons.

* Outermost Shell: The outermost shell (n=3) is the valence shell, and it contains the electrons involved in chemical bonding.

Let me know if you have any other questions!