十酸化四リン

解説リンの酸化物で無色の固体．リン原子が四面体型に配置された分子で分子式P4O10．昔はその組成から五酸化二リンP2O5とよばれたが，現在は使わない．無水リン酸という呼称も望ましくない．

一般的な説明Phosphorus pentoxide forms three solid modifications, of which the metastable M form is the ordinary commercial P2O5. This modification crystallizes as rhombohedra with a molecular lattice (P4O10) and sublimes readily at 250°C and 10 mm. Above 260°C and even more quickly above 500°C, form M changes into form R. The latter crystallizes in a three-dimensional atomic lattice of PO4 tetrahedra and is less volatile. A form S crystallizes in a layer lattice, and a few vitreous forms are also known. Modification M is brittle; R and S form hard crystals, which deliquesce after a few hours in the air and undergo considerable swelling in water. The density of R is 2.72, and that of M is 2.30 (calculated from x-ray data).