Ok, I asked this question a looooong time ago, (it may have been at the 'Point'), and I never did get an agreed upon answer.

If H2O2 is Hydrogen Peroxide, what is H2O?

I took a semester of high school chemistry so I know there are naming conventions based on things like atoms per molecule, or the ratio of oxygen in a molecule, etc. Obviously I have lost all that knowledge and am relying on all you avid chemists to at least come to a consensus on the chemical name for water.

While we're at it, why is Oxygen nearly always represented as O2, and not just O? I know that the 2 means two atoms per molecule but isn't one atom of Oxygen still oxygen?

First the oxygen. Basicallly, we write it as O₂ because that is how it actually exists. The oxygen that you breathe exists as pairs of oxygen atoms bound together. Oxygen atoms don't like to be alone (don't you love how chemists always talk about chemicals as if they have emotional issues?). The same goes for hydrogen, but not for helium (helium is anti-social ), so you would see those represented as H₂ and He, respectively.


Now, on to water. First off, no self-respecting chemist would refer to as anything but "water" or maybe "H two O" unless they were making some sort of joke. But, if they did, it would be dihydrogen monoxide. A case might be made for hydrogen hydroxide, but I think this is a worse choice. The first name treats it as a molecular compound and the second treats it as an ionic compound.



These questions highlight two things about naming chemicals:

Many chemicals go by a common name (especially those that are older than our knowledge of what they actually are, such as water, or those that would have extremely long names, such as proteins)

The most common or earliest known form of an element is usually given the same name as the element (So, the relatively uncommon and comparatively recently discovered O₃ is called ozone, but the very common and longer-known O₂ is just oxygen.

[This message was edited by methos5000 on 05-30-03 at 12:23 PM.]

Thanks methos. I was going to ask you how you did subscript but then I forgot I wasn't in the D_R.

I prefer dihydrogen monoxide (H2O) However it isn't really used that much - But it does make for some interesting looks when you tell people that your well has been found to contain high quantities of dihydrogen monoxide - especially after you give them a glass of water.



David

I'm still confused. If the prefix "di" means 2, then why isn't H₂O₂ called 'dihydrogen peroxide'? Or for that matter 'dihydrogen dioxide'? What does "per" indicate?

There are 2 ways to name inorganic compounds.

The first is used for molecular compounds. For this, you just add prefixes to show the numbers of each atom. This would make H₂O₂ dihydrogen dioxide, if it were a molecular compound.

For ionic compounds, however, You simply list the cation (positive ion) and then the anion (negative ion). Because you know the charge of each ion, you can figure out the proportions without prefixes. The hydrogen cation (H¹⁺) is simply called hydrogen in this naming system. The O₂^2- ion, is called peroxide. Putting them together, you end up with hydrogen peroxide. You know there must be 2 hydrogen ions for each peroxide ion to belance out the charge. Similarly, the OH^1- ion is called hydroxide. So, if water were to be named as an ionic compound, it would be called hydrogen hydroxide.

So why is O₂^2- called peroxide? Per- indicates that an atom in the ion is in its highest oxidation state (most negative charge). Peroxide is oxygen in its highest oxidation state.

I'd give my left particle to be that smart. Thanks for explaining methos.

Ditto....

An alternate view of Dihydrogen Monoxide.

DHMO.ORG

Mike b. (AKA Byter)

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