There's a small error in the electron configuration you provided. Chlorine's electron configuration is [Ne] 3s² 3p⁵, not [Ne] 3s² 3p⁶5.

Here's how to determine the number of valence electrons:

* Valence electrons are the electrons in the outermost energy level. For chlorine, the outermost energy level is the third energy level (n=3).

* The 3s² and 3p⁵ subshells are both in the third energy level.

* Add the number of electrons in these subshells: 2 (from 3s²) + 5 (from 3p⁵) = 7 valence electrons.

Therefore, a chlorine atom has 7 valence electrons.