phosphorus

i just only know that
It ignites spontaneously in air at about 50 °C, and at much lower temperatures if finely divided. This combustion gives phosphorus (V) oxide:

P₄ + 5O₂ -> P₄O₁₀

Because of this property, white phosphorus is used as a weapon.

this is because of strain in sp3 hybridised p₄ molecule.the angle bw p &p is only 60°
as compared to the normal tetrahedral angle of 128°.thus it extrmely unstable and hence reactive.this is the teason it has a low ignition temp and catches fire spontaneously..

okay thanks a lot...

IN WHITE PHOSPHORUS MOLECULE(TETRAHEDRAL STRUCTURE) THE 4 P ATOMS ARE LOCATED AT THE 4 CORNERS OF A TETRAHEDRON.THE ANGLE BETWEEN 2 P ATOMS IS 60°BUT THE ANGLE BETWEEN 2 p ORBITALS SHOULD BE 90°,SO DUE TO INTERNAL STRAIN IT HAS A TENDANCY TO BREAK INTO ATOMS.SO ON APPLYING SLIGHT AMOUNT OF HEAT ENERGY IT STARTS BURNING.