Ammonium

Ammonium is the polyatomic cation NH₄⁺, formed when ammonia accepts a proton. It occurs in many ionic compounds and in aqueous acid–base systems.

Brønsted–Lowry acid–base theory: Brønsted–Lowry theory defines acids as proton donors and bases as proton acceptors. It describes ammonia accepting a proton to become ammonium.
Ammonium nitrate: Ammonium nitrate is the ionic compound NH₄NO₃, widely used as a nitrogen fertilizer and oxidizer. It supplies nitrogen in agriculture and illustrates ammonium’s role in fertilizer salts.
Polyatomic ion: A polyatomic ion is a charged group of covalently bonded atoms that behaves as a single unit in compounds. Ammonium is a compact example of a polyatomic cation.
Hydronium: Hydronium is the polyatomic cation H₃O⁺, formed when water accepts a proton. It is the oxygen-centered counterpart to nitrogen-centered ammonium.
Joseph Priestley: Joseph Priestley was an English natural philosopher whose experiments identified several gases, including ammonia. His work on alkaline air helped establish ammonia chemistry from which ammonium is derived.
Tetrahedral molecular geometry: Tetrahedral molecular geometry places four bonds around a central atom at angles near 109.5 degrees. Four N–H bonds give ammonium its tetrahedral shape.
Ammonium sulfate: Ammonium sulfate is the ionic compound (NH₄)₂SO₄, used chiefly as a nitrogen and sulfur fertilizer. Its agricultural use shows how ammonium salts deliver plant-available nitrogen.
Formal charge: Formal charge is an accounting convention that assigns valence electrons to atoms in a Lewis structure. It tracks the positive charge associated with ammonium’s nitrogen.
Methylammonium: Methylammonium is the cation CH₃NH₃⁺, formed by protonating methylamine. It resembles ammonium but replaces one hydrogen with a methyl group.
Ammonium chloride: Ammonium chloride is the ionic compound NH₄Cl, historically known as sal ammoniac. This familiar salt helped give the ammonium group its name.

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