The atomic number of chlorine is 17. Hence it has 2 electrons in its inner-most shell, 8 electrons in its second shell and 7 electrons in outer-most shell respectively.
Electrons in the outer shells that are not filled are called valence electrons.
The atomic number of chlorine is 17. Hence it has got 7 electrons in its outermost shell.
There are 7 valence electrons in the chlorine atom.