Writing electron configurations

Here are some extra tidbits about ions for your chemistry reading pleasure:

✓ You can write electron configurations and energy level diagrams for ions. The neutral sodium atom (11 protons) has an electron configuration of 1s²2s²2p⁶3s¹. The sodium  cation has lost an electron the valence electron, which is farthest away from the nucleus (the 3s electron, in this case). The electron configuration of Na⁺ is 1s²2s²2p⁶.

✓ The electron configuration of the chloride ion (Cl^–) is 1s²2s²2p⁶3s²3p⁶. This is the same electron configuration as the neutral argon atom. If two chemical species have the same electron configuration, they’re said to be isoelectronic. Figuring out chemistry requires learning a whole new language, eh?

✓ This section has been discussing monoatomic (one atom) ions. But polyatomic (many atom) ions do exist. The ammonium ion, NH₄⁺, is a polyatomic ion, or specifically, a polyatomic cation. The nitrate ion, NO₃^–, is also a polyatomic ion, or specifically, a polyatomic anion.