Question

What is the name for `P_2O_5`?

Answer 1

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 oxygen

The '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.

Answer 2

`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 compound's 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.

Answer 3

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.

For its avidity of water, it is one of the most powerful known dehydrating agent.