NH4X

NH4X denotes salts formed from the ammonium cation NH4+ and a halide anion X−, where X represents a halogen: fluorine, chlorine, bromine, or iodine. The family includes ammonium fluoride (NH4F), ammonium chloride (NH4Cl), ammonium bromide (NH4Br), and ammonium iodide (NH4I). These are ionic solids that are typically white crystals and soluble in water. In the solid state they form lattice structures governed by Coulombic attraction between NH4+ and X−, with lattice energy and thermal behavior varying with the halide.

They are commonly prepared by neutralization of aqueous ammonia with hydrohalic acids: NH3 + HX → NH4X, or by combining ammonium salts with halide sources. These salts are generally stable at room temperature and can be isolated as crystalline solids or in aqueous solution.

All NH4X salts are soluble in water and form mildly acidic solutions because NH4+ acts as a weak acid. On heating, they decompose to release ammonia and the corresponding hydrogen halide: NH4X → NH3 + HX. The decomposition behavior becomes more facile down the halide series, and some salts may sublimate or decompose before melting.

Uses vary by halide. NH4Cl is widely used as a nitrogen fertilizer and as a flux in metalworking. NH4F serves as a source of fluoride for glass etching and various surface treatments. NH4Br and NH4I are mainly employed as reagents in chemical synthesis and qualitative analysis, with more specialized roles in research and industry.

Safety considerations include their irritant properties; exposure to dust or fumes should be minimized. Heating or decomposition releases ammonia and hydrogen halides, so appropriate ventilation and protective equipment are advised.