OP

OP, O.P., Op, or Op. may refer to:

Arts

Internet and gaming

Mathematics

Organizations

Dominican Order

The Order of Preachers (Latin: Ordo Praedicatorum, hence the abbreviation OP used by members), more commonly known after the 15th century as the Dominican Order or Dominicans, is a Roman Catholic religious order founded by the Spanish priest Saint Dominic de Guzman in France and approved by Pope Honorius III (1216–27) on 22 December 1216. Membership in this "mendicant" Order includes friars, nuns, active sisters, and lay or secular Dominicans (formerly known as tertiaries, though recently there has been a growing number of Associates, who are unrelated to the tertiaries) affiliated with the Order.

Founded to preach the Gospel and to combat heresy, the teaching activity of the order and its scholastic organization placed the Preachers in the forefront of the intellectual life of the Middle Ages. The order is famed for its intellectual tradition, having produced many leading theologians and philosophers. The Dominican Order is headed by the Master of the Order, who is currently Bruno Cadoré. Members of the order generally carry the letters O.P., standing for Ordinis Praedicatorum, meaning of the Order of Preachers, after their names.

Phosphorus pentoxide

Phosphorus pentoxide is a chemical compound with molecular formula P₄O₁₀ (with its common name derived from its empirical formula, P₂O₅). This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desiccant and dehydrating agent.

Structure

Phosphorus pentoxide crystallizes in at least four forms or polymorphs. The most familiar one, a metastable form, shown in the figure, comprises molecules of P₄O₁₀. Weak van der Waals forces hold these molecules together in a hexagonal lattice (However, in spite of the high symmetry of the molecules, the crystal packing is not a close packing). The structure of the P₄O₁₀ cage is reminiscent of adamantane with T_dsymmetry point group. It is closely related to the corresponding anhydride of phosphorous acid, P₄O₆. The latter lacks terminal oxo groups. Its density is 2.30 g/cm³. It boils at 423 °C under atmospheric pressure; if heated more rapidly it can sublimate. This form can be made by condensing the vapor of phosphorus pentoxide rapidly, the result is an extremely hygroscopic solid.