What IS a chemical?


You at the back there! Get your nose out of that dictionary and pay attention!

What do we mean when we use the word “chemical”? It seems like a simple enough question, but is it, really? I write about chemicals all the time – in fact my last WhatCulture article was about just that – and I’ve mentioned lots of different definitions before. But I’ll be honest, some of them have bothered me.

I don’t often like the definitions you find in dictionaries. Lexicography and chemistry don’t seem to be common bedfellows, and dictionary compilers haven’t, generally speaking, spent their formative years being incessantly nagged by weary chemistry teachers about their choice of vocabulary.

For example, in the Cambridge Dictionary we find:
any basic substance that is used in or produced by a reaction involving changes to atoms or molecules.”

Hm. Firstly, “basic” has a specific meaning in chemistry. Obviously the definition doesn’t mean to imply that acids aren’t chemicals, but it sort of accidentally does. Then there’s the implication that a chemical reaction has to be involved. So inert substances aren’t chemicals? Admittedly, “used in” doesn’t necessarily imply reacts – it could be some sort of inert solvent, say – but, again, it’s bothersome. Finally, “atoms or molecules”. Ionic substances not chemicals either, then?

Yes, it’s picky, but chemists are picky. Be glad that we are. A misplaced word, or even letter, on a label could have serious consequences. Trust me, you do not want to mix up the methanol with the ethanol if you’re planning cocktails. Similarly, fluorine is a whole other kettle of piranhas compared to fluoride ions. This stuff, excuse the pun, matters.

Dictionary definitions have their problems.

Dictionary definitions have their problems.

Let’s look at some more definitions (of the word as a noun):

The Free Dictionary tells us that a chemical is:
“A substance with a distinct molecular composition that is produced by or used in a chemical process.”

Merriam Webster says:
“of, relating to, used in, or produced by chemistry or the phenomena of chemistry <chemical reactions>”

And Dictionary.com goes with the simple:
“a substance produced by or used in a chemical process.”

That idea that a chemical reaction must be involved somehow seems to be pervasive. It’s understandable, since that’s the way the word is mostly used, but it’s not really right. Helium, after all, is still very much a chemical, despite being stubbornly unreactive.

Possibly the best of the bunch is found in the Oxford Living Dictionary:
“A distinct compound or substance, especially one which has been artificially prepared or purified.”

Not bad. Well done Oxford. No mention of chemical reactions here – it’s just a substance. We do most often think of chemicals as things which have been “prepared” somehow. Which is fair enough, although it can lead to trouble. In particular, ridiculous references to “chemical-free” which actually mean “this alternative stuff is naturally-occurring.” (Except of course it often isn’t: see this article about baby wipes.) The implication, of course, is that thing in question is safe(r), but there are lots and lots of very nasty chemicals in nature: natural does not mean safe.

You keep using that word. I do not think it means what you think it means.

Sometimes people will go the other way and say “everything is chemicals.” We know what this means, but it has its problems, too. Light isn’t a chemical. Sound isn’t a chemical. All right, those are forms of energy. What about neutrinos, then? Or a single proton? Or a single atom? Or, going the other way, some complicated bit of living (or once living) material? In one debate about this someone suggested to me that a “chemical was anything you could put in a jar,” at which point I pedantically said, “I keep coffee in a jar. Is that a chemical?” Obviously there are chemicals in coffee, it works from the “everything is chemicals” perspective, but it’s a single substance that’s not a chemical.

Language is annoying. This is why chemists like symbols and numbers so much.

Anyway, what have we learned? Firstly, something doesn’t necessarily have to be part of a chemical reaction to be a chemical. Secondly, we need to include the idea that it’s something with a defined composition (rather than a complex, variable mixture, like coffee), thirdly that chemical implies matter – light, sound etc don’t count, and fourthly that it also implies a certain quantity of stuff (we probably wouldn’t think of a single atom as a chemical, but collect a bunch together into a sample of gas and we probably would).

So with all that in mind, I think I shall go with:

So what IS a chemical?

A chemical is…

(Drum roll please….)

Any substance made of atoms, molecules and/or ions which has a fixed composition.

I’m not entirely convinced this is perfect, but I think it more or less works.

If you have a better idea, please do comment and let me know!

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17 thoughts on “What IS a chemical?

  1. This is fantastic. I find myself leaning to the everything is chemicals end but mostly because the place I see “chemical free” is most often food. Which always makes me want to snarkily respond that I don’t want to pay for something that doesn’t exist. While your coffee in a jar may not be a chemical it is not chemical free. So I’ll try to do better in my snarking in my head at the farmers market!

    Liked by 1 person

  2. Hi Kat! Well, that’s probably the best definition so far. Talking of the difference a letter makes, don’t mix up Ammonal with Ammonol. Apparently during the first world war a spelling mistake nearly sent the wrong stuff to the front line. Or perhaps they did send the wrong stuff. Ammonol was an analgesic, perhaps a few tonnes would have cured the headaches after the Ammonal went off.

    Liked by 1 person

  3. Kat
    In school education, we used to have (and still do on the tin) sodium hypochlorite (bleach) and sodium chlorate (weed killer). Then we tried to educate students and have sodium chlorate(I) and sodium chlorate(V). I was told this was IUPAC nomenclature. Even school teachers and technicians got them confused. Looking at the IUPAC nomenclature on the European Chemical Agency, chlorate(I) does not appear under IUPAC names. Sometimes we confuse ourselves!
    Of course we then have interstitial chemicals such as iron(II) sulfide, and clathrates which have a variable composition but perhaps we had better not go there. “All terribly confusing” as Neddy Seagoon would say but that is what makes chemistry fascinating.

    Liked by 1 person

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  6. Can’t help it:
    Nitrate NO_3 Nitrite NO_2
    Sulfate SO_4 Sulfite SO_3
    Phosfate PO_4 Phosfite PO_3
    My rule of the thumb (is that correct English? Sorry, no native speaker) is that the -ite has one O less than the -ate


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