Arsenic: reactions of elements
Reaction of arsenic with air
Arsenic is stable in dry air, but the surface oxidizes slowly in moist air to give a bronze tarnish and finally a black covering to the element. When heated in air, arsenic ignites "arsenic trioxide" - actually tetraarsenic hexaoxide, As4O6. This is accompanied by phosphorescence under some conditions. When heated in oxygen, arsenic ignites in oxygen to form "arsenic pentoxide" - actually tetraarsenic decaoxide, As4O10, and As4O6.
4As(s) + 5O2(g) → As4O10(s)
4As(s) + 3O2(g) → As4O6(s)
Reaction of arsenic with water
Arsenic does not react with water in the absence of air under normal conditions.
Reaction of arsenic with the halogens
Arsenic reacts with fluorine, F2, to form the gas pentafluoride arsenic(V) fluoride.
2As(s) + 5F2(g) → 2 AsF5(g) [colourless]
Arsenic reacts under controlled conditions with the halogens fluorine, F2, chlorine, Cl2, bromine, Br2, and iodine, I2, to form the respective trihalides arsenic(III) fluoride, AsF3, arsenic(III) chloride, AsCl3, arsenic(III) bromide, AsBr3, and arsenic(III) iodide, AsI3.
2As(s) + 3F2(g) → 2AsF3(l) [colourless]
2As(s) + 3Cl2(g) → 2AsCl3(l) [colourless]
2As(s) + 3Br2(g) → 2AsBr3(s) [pale yellow]
2As(s) + 3I2(g) → 2AsI3(s) [red]