I am inexperienced with this topic aswell,
but i just want to propose something...
has 16 protons and needs to attract 18 electrons, the electrons are further away from the nucleus than they would be in the case of the Potassium ion K+
where 19 protons need to attract 18 electrons. The protons act as a magnet, and attract the electrons closer to the nucleus.
Can anyone correct me, or contradict me? or am i right....
O, Cl, K+
, S -2