How is ammonium (NH4+) an ionic bond?

Question

I was taught that ionic is metal/transition metal + non-metal. N is a non-metal and H is a non-metal, so I thought NH4+ would be a covalent. However, on a quiz today, we were supposed to count all the ionic bonds and I got this wrong because I didn't count NH4+.

How is NH4+ an ionic bond instead of a covalent one?

Answer 1

I would agree with you that NH₄⁺ (the ammonium cation) is a covalent molecule. If it were associated with an anion to make the corresponding salt, then it would be an ionic compound. You should ask your teacher to give you credit or to explain how/why NH₄⁺ is not covalent.

Answer 2

You are correct in thinking that NH4+ is covalent. However, this only applies to the bonds that make up the NH4+ itself. The molecule as a whole is charged, making an ion and thus, will form ionic bonds to non-metals (such as Cl^-, O^2-, and F^-). It will also form ionic bonds with polyatomic ions(NH4+ is also a polyatomic ion), such as NO₃^-, SO₄^2-, and PO₄^3-. Therefore, I would change your definition that an ionic bond is metal/transition metal + non-metal to be broader to include bonds between cation ions and anion ions. Hopefully, this explanation clears up any confusion you may have had.