PHOSPHORUS, ARSENIC AND ANTIMONY
The bigger elements in the same group (15) as nitrogen are usually known as 'pnictogens' and their compounds with metals as 'pnictides'. Although the elements form some compounds same to those of nitrogen, there are widely pronounced differences, as is found in other nonmetal groups.
Phosphorus is moderately abundant in the Earth's crust as the phosphate ion; the major mineral source is apatite Ca5 (PO4)3(F,Cl,OH), the notation (F,Cl,OH) being used to display that OH- and F-, Cl- can be define in varying proportions. Antimony and arsenic are much rarer. They find in minerals such as stibnite Sb2S3 and realgar As4S4, but are widely collect as byproducts from the processing of sulfide ores of other elements. Elemental P is finding by reduction of calcium phosphate. The complex reaction likes to:
Most phosphates are required more directly without conversion to the element. Phosphorus has greater allotropes. It is most frequently encountered as white phosphorus, which have tetrahedral P4 molecules with Td symmetry. Other forms, which are more stable and reliable thermodynamically but kinetically harder to build, contain polymeric networks with three-coordinate P. White phosphorus is highly toxic and reactive.