Tantalum

Tantalum does not react wwith most acids, but does dissolve in hydrofluoric acid, HF, and oleum (a solution of sulphur trioxide, SO₃, in sulphuric acid, H₂SO₄; also called fuming sulphuric acid).

Tantalum is passivated by a thin layer of tantalum oxides on the surface, and does not otherwise react with air under normal conditions.

Tantalum reacts with halogens upon heating, forming the corresponding Ta(V) halides.

2 Ta(s) + 5 F₂(g) TaF₅(s) [white]
2 Ta(s) + 5 Cl₂(g) TaCl₅(l) [white]
2 Ta(s) + 5 Br₂(g) TaBr₅(s) [pale yellow]
2 Ta(s) + 5 I₂(g) TaI₅(s) [black]

Tantalum does not react with water under normal conditions.