2 questions about ionic bonding

[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~! =)

 

[Blueshift5]

I can provide some explanations for your questions about ionic bonding.

1. The increase in size of anions, such as the chloride anion, when they achieve a full valence electron shell is due to the repulsion between the negatively charged electrons. When the anion gains an electron to fill its valence shell, the negative charges repel each other, causing the anion to expand in size. This is known as the electron-electron repulsion. Additionally, the added electron also increases the overall negative charge of the anion, which can also contribute to its increased size.

2. The naming of ionic compounds involving polyatomic ions follows a specific set of rules. The cation, or positively charged ion, is always named first, followed by the anion, or negatively charged ion. In the case of (NH4)2CO3, ammonium is the cation and carbonate is the anion. The reason for this naming convention is because the cation is usually a metal, while the anion can be a nonmetal or a polyatomic ion. In the case of ammonium, it is a positively charged ion made up of nitrogen and hydrogen, and is commonly treated as a single unit in chemical reactions. Therefore, it follows the same naming rules as a metal cation.