ammonium group

ammonium group in chemistry, a positively charged nitrogen atom joined by single bonds to four other atoms or groups. The simplest ammonium group, NH ₄⁺ , is formed by protonation of ammonia , NH ₃ , e.g., by its reaction with hydrogen chloride, HCl, to form ammonium chloride, NH ₄ Cl, an ammonium compound. Organic ammonium compounds are formed by the reaction of an alkyl halide with an amine (see amino group ), for example, ethyl chloride, C ₂ H ₅ Cl, reacts with triethylamine, (C ₂ H ₅ ) ₃ N, to form tetraethyl ammonium chloride, (C ₂ H ₅ ) ₄ N ⁺ Cl ^- . They are also formed by reaction of an amine with a mineral acid or by reaction of an alkyl halide with ammonia.