Why Do Anions Increase in Size and How Are Ionic Compounds Named?

[bennington]

1. Why do anions, such as the chloride anion, increase in size when they achieve a full valence electron shell? This does not make sense to me because there is no new shell that is added.
2. How would you name ionic compunds involving polyatomic ions? My book says that (NH4)2CO3 would be ammonium carbonate. This also does not make sense to me because ammonium is not a metal , so there is no reason that it should go first.

Thanks for the help!

 

[Spherical]

1. There's an increased electron-electron repulsion due to the extra negative charge, thus more repulsion and increased atomic size.
2. I think you're thinking "ionic" too specifically to only "metal" ions. Cations are normally metals, but not all of them. Normally, naming ionic compounds with radicals are just simply naming the cation, (the charge if its multivalent), and the anion after it; it has nothing to do with metals or gases. And that's how ammonium carbonate should be named, so there's nothing wrong with the textbook.

Hope it helps~! =)