Ammonium: Definition, Structure & Formula

Instructor: LaRita Williams

LaRita holds a master's degree and is currently an adjunct professor of Chemistry.

In this lesson, we will define ammonium and take a closer look at its bonding structure, geometrical shape, and chemical formula. We also discuss the acid-base reaction that forms ammonium.

What is Ammonium?

If you're a florist, it's your job to familiarize yourself with the names and appearances of several different types of flowers. If you're a chef, it's your job to familiarize yourself with the names and appearances of several different types of foods. And if you're a chemist, it's your job to learn the names and appearances of various chemical compounds. Ammonium is one such compound.

Ammonium is a polyatomic cation with the chemical formula NHsub4^+. To better understand what that means, let's break down a couple of terms. The term 'cation' refers to an electron deficient species that carries a positive charge. The term 'polyatomic' refers to compounds that contains two or more different atoms functioning together as a unit. In the case of ammonia, there are four hydrogen atoms bonded to one central nitrogen atom carrying an overall charge of +1.

Formation and Formula of Ammonium

The ammonium ion is formed when a neutral ammonia compound is protonated, or takes on an additional positively charged hydrogen atom. You can see how this plays out below in Equation 1. Ammonia, on the far left, is a weak base with the chemical formula NHsub3. When this neutral compound takes on a hydrogen atom with a positive charge (proton), it gains that atom as well as its positive charge and forms NHsub4^+.

Formation of Ammonium

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