Question

Why is no. of valence electrons in Cl- ion 8?

Answer 1

The atomic number of chlorine is 17 and its electronic configuration is 2, 8, 7. Thus there are 7 electrons in the valence shell of chlorine. When chlorine forms a chloride ion, it accepts an electron.

1/2 Cl₂ + e^- → Cl^-

Thus, on accepting an electron, chlorine forms chloride ion which has one electron more than chlorine atom and its electronic configuration is 2, 8, 8. Hence there are 8 electrons in the valence shell of Cl^- ion.