What is the name for P_2O_5?
The name is diphosphorus pentoxide.Binary compounds with oxygen in them have oxide as a last name.The first name is phosphorus.We give the numbers of each atom:di (=2) phosphorus penta (=5) oxide, which means: 2 phosphorus together with 5 oxygenThe a of penta is omitted when it comes before o as in oxide. Often the di- is also omitted (as the other compound also starts with di-), and it is called just phosphorus pentoxide.Extra :An older name would be phosphoric oxide, P_2O_5, as opposed to phosphorous oxide P_2O_3, which is the other possibility.The systematic name for P_2O_5 is phosphorus(V) oxide. The numeral V signifies the oxidation number of phosphorus, which is +5.In the same way P_2O_3 is called phosphorus(III) oxide, as the oxidation number of phosphorus is +3.
P_2O_5 is commonly named phosphorus pentoxide. An interesting fact about phosphorus pentoxide is that P_2O_5 is actually its empirical formula; its molecular formula is actually P_4O_10. The compounds name however was derived from its empirical formula, not from its molecular formula. The standard name for this compound is actually diphosphorus pentoxide. The di- prefix is used to show that the compound contains two phosphorus atoms and the penta- prefix is used to show it contains five oxygen atoms.
Phosphorus pentoxide is the most used name for P_4O_10, the white molecular solid whose empirical formula is P_2O_5. It is the anhydride of phosphoric acid. This is the image of the molecule from wikipedia.