Terbium: reactions of elements
Reaction of terbium with air
Terbium metal tarnishes slowly in air and burns readily to form a terbium oxide which has the approximate formula Tb4O7.
8Tb + 7O2 → 2Tb4O7
Reaction of terbium with water
The silvery white metal terbium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form terbium hydroxide, Tb(OH)3, and hydrogen gas (H2).
2Tb(s) + 6H2O(g) → 2Tb(OH)3(aq) + 3H2(g)
Reaction of terbium with the halogens
Terbium metal reacts with all the halogens to form terbium(III) halides. So, it reacts with fluorine, F2, chlorine, Cl2, bromine, I2, and iodine, I2, to form respectively terbium(III) bromide, TbF3, terbium(III) chloride, TbCl3, terbium(III) bromide, TbBr3, and terbium(III) iodide, TbI3.
2Tb(s) + 3F2(g) → 2TbF3(s) [white]
2Tb(s) + 3Cl2(g) → 2TbCl3(s) [white]
2Tb(s) + 3Br2(g) → 2TbBr3(s) [white]
2Tb(s) + 3I2(g) → 2TbI3(s)
Reaction of terbium with acids
Terbium metal dissolves readily in dilute sulphuric acid to form solutions containing the very pale pink aquated Tb(III) ion together with hydrogen gas, H2. It is quite likely that Tb3+(aq) exists as largely the complex ion [Tb(OH2)9]3+
2Tb(s) + 3H2SO4(aq) → 2Tb3+(aq) + 3SO42-(aq) + 3H2(g)