Technetium

Technetium is insoluble in hydrochloric acid (HCl) and hydrofluoric acid (HF). It does dissolve in nitric acid, HNO₃, and concentrated sulphuric acid, H₂SO₄, forming solutions of pertechnetic acid, HTcO₄.

Technetium tarnishes very slowly in moist air, and upon heating with oxygen, O₂, forms technetium(VII) oxide, Tc₂O₇.

4 Tc(s) + 7 O₂(g) 2 Tc₂O₇(s)

Technetium reacts with fluorine upon heating, forming a mixture of Tc(IV) and Tc(VII) fluoride.

Tc(s) + 3 F₂(g) TcF₆(s)
2 Tc(s) + 7 F₂(g) 2 TcF₇(s)

Technetium reacts with water [1]:

Tc(s) + 2 H₂O(l) TcO₂(s) + 4 H⁺(aq) + 4 e⁻                E° = -0.272 V
TcO₂(s) + H₂O(l) TcO₃(s) + 2 H⁺(aq) + 2 e⁻              E° = -0.757 V
Tc²⁺(aq) + 4 H₂O(l) TcO₄⁻(aq) + 8 H⁺(aq) + 5 e⁻        E° = -0.500 V