Barium: reactions of elements
Reaction of barium with air
Barium is a silvery white metal. The surface of barium 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. Once ignited, barium metal burns in air to give a mixture of white barium oxide, BaO, and barium nitride, Ba3N2. Barium oxide is more normally made by heating barium carbonate. The superoxide BaO2 apparently is also formed in this reaction. Barium, three places below magnesium in the periodic table is more reactive with air than magnesium.
2Ba(s) + O2(g) → 2BaO(s)
Ba(s) + O2(g) → BaO2(s)
3Ba(s) + N2(g) → Ba3N2(s)
Reaction of barium with water
Barium reacts readily with water to form barium hydroxide, Ba(OH)2 and hydrogen gas (H2). The reaction is quicker than that of strontium (immediately above barium in the periodic table) but probably slower than that of radium (immediately below barium in the periodic table).
Ba(s) + 2H2O(g) → Ba(OH)2(aq) + H2(g)
Reaction of barium with the halogens
I expect barium is very reactive towards the halogens, but I've not yet found explicit references to that effect. So, it is epxected that chlorine, Cl2 bromine, Br2, or iodine, I2, would burn to form the dihalides barium(II) chloride, BaCl2, barium(II) bromide, BaBr2, and barium(II) iodide, BaI2 respectively. The reactions with bromine and with iodine wolud probably require heat.
Ba(s) + Cl2(g) → BaCl2(s)
Ba(s) + Br2(g) → BaBr2(s)
Ba(s) + I2(g) → BaI2(s)