Ammonium is a polyatomic ion, meaning it is a group of atoms bonded together with an overall charge. It has the formula NH₄⁺.

Atomic numbers refer to individual elements. Therefore, ammonium doesn't have an atomic number.

Here's a breakdown of the elements within ammonium:

* Nitrogen (N): Atomic number 7

* Hydrogen (H): Atomic number 1

Ammonium is formed when a nitrogen atom bonds with four hydrogen atoms, gaining a positive charge.