Chemical reactions of the elements
Reaction of thallium with air
Freshy cut thallium tarnishes slowly to give a grey oxide film that protects the remaining metal from further oxidation. When heated strongly to red heat in air, poisonous thallium(I) oxide is formed.
2Tl(s) + O2(g) → Tl2O(s)
Reaction of thallium with water
Thallium seems not to react with air-free water. Thallium metal tarnishes slowly in moist air or dissolves in water to give poisonous thallium(I) hydroxide.
2Tl(s) + 2H2O(l) → 2TlOH(aq) + H2(g)
Reaction of thallium with the halogens
Thallium metal reacts vigorously with fluorine, F2, chlorine, Cl2, and bromine, Br2, to form the dihalides thallium(III) fluoride, TlF3, thallium(III) chloride, TlCl3, tand hallium(III) bromide, TlBr3, respectively. All these compounds are poisonous.
2Tl(s) + 3F2(g) → 2TlF3(s) 
2Tl(s) + 3Cl2(g) → 2TlCl3(s) 
2Tl(s) + 3Br2(l) → 2TlBr3(s) 
Reaction of thallium with acids
Thallium dissolves only slowly in sulphuric acid, H2SO4, or hydrochloric acid, HCl, because the poisonous thallium(I) salts produced are not very soluble.
Reaction of thallium with bases