铵

Left-side metal radical, the simplified five-stroke form of 金. 铵 is the Chinese name for ammonium, a chemistry coinage: the metal radical signals an inorganic cation, putting 铵 in the modern element/compound family with 钠 sodium, 钾 potassium, 锌 zinc. Most chemistry-related characters get this radical even when no actual metal is involved.

Right side 安 supplies the sound: ān → ǎn with tone shift only, the cleanest possible phonetic match. 安 was chosen for the modern element-name 铵 specifically to mimic the 'amm-' of ammonium / Latin ammoniacum. Same phonetic family: 按 to press, 案 case/file, 鞍 saddle.