Ammonium ion (NH₄⁺)

Ammonium is one nitrogen atom bonded to four hydrogen atoms, and the whole group carries a 1+ charge. It forms when an ammonia molecule, NH₃, uses its spare pair of electrons to grab a hydrogen ion, H⁺, which brings its positive charge along. You meet it in fertilizers, smelling salts and any lab reaction where ammonia meets an acid.

• Ammonium is the most common positive polyatomic ion, so in formulas it takes the place of a metal ion, as in ammonium chloride, NH₄Cl.
• Its -ium ending marks a cation, the same ending used for hydronium, H₃O⁺.
• Ammonium nitrate, NH₄NO₃, and ammonium sulfate, (NH₄)₂SO₄, are two of the most widely used nitrogen fertilizers.

Compounds that contain ammonium

Other ions with a +1 charge