Radium: reactions of elements
Reaction of radium with air
Radium is a silvery white metal. The surface of radium metal is covered with a thin layer of oxide that helps protect the metal from attack by air, but to a lesser extent than the corresponding layer in magnesium. I'm not sure if this reaction has been done, but once ignited, radium metal is likely to burn in air to give a mixture of white radium oxide, RaO, and radium nitride, Ra3N2. The superoxide RaO2 is also likely to form in this reaction. Radium, four places below magnesium in the periodic table is more reactive with air than magnesium.
2Ra(s) + O2(g) → 2RaO(s)
Ra(s) + O2(g) → RaO2(s)
3Ra(s) + N2(g) → Ra3N2(s)
Reaction of radium with water
Radium probably reacts very readily with water to form radium hydroxide, Ba(OH)2 and hydrogen gas (H2). The reaction is expected to be quicker than that of barium (immediately above radium in the periodic table).
Ra(s) + 2H2O(g) → Ra(OH)2(aq) + H2(g)
Reaction of radium with the halogens
I'm not sure that radium has been reacted directly with the halogens, although certainly two of the expected products radium(II) chloride and radium(II) bromide are known.