Question

Which of the following, in Fig. correctly represents $$\mathrm{Cl}^{-}$$ ion (Atomic number of chlorine = 17).

Answer 1

Chlorine has 17 electrons with configuration $$2, 8, 7$$. The chloride ion, $$\mathrm{Cl}^{-}$$, has gained one electron, so it has 18 electrons arranged as $$2, 8, 8$$. Therefore the correct diagram is the one showing 2 electrons in the K-shell, 8 in the L-shell and 8 in the M-shell.