[nojnoj]

Sorry if this is a FAQ, but ... I'm a non-chemist looking for an answer to a simple but slightly obtuse question.

Is there a term to describe the striking "non-linearity"* of chemical reactions, specifically the way that reactants combine to form products whose properties are totally different from each other? IOW, the products of a reaction being more or less (or even the opposite) of the "sum" of their parts?

Obvious examples to a chemistry noob like me would be Na and Cl forming common salt, and C and N forming the cyanide ?radical; the former reaction seeing dangerous (to us) elements  combining to form something harmless/useful, and the latter the exact opposite.

It just seems such an arbitrary phenomenon, in the sense that for many reactions the initial ingredients' properties are no indicator of the resulting ones.



* qualitatively speaking, rather than strictly mathematical.

[Schrödinger]

I can give you plenty more examples like the ones you gave in the above post.
Reason : This is NOT physics... Your "rules of superposition" do not work here. There is no mathematics involved here.
All I can say is : That is Chemistry for you!!

[nojnoj]

This is NOT physics... Your "rules of superposition" do not work here. There is no mathematics involved here.
All I can say is : That is Chemistry for you!!

Thanks for the reply. How did you guess I came from a physics background?!

I'll just have to adjust to the dangerous anarchy of electron-shell "social politics"!   

[cth]

Physical properties are the results of interactions between atoms and molecules. For example, boiling temperature of water only makes sense if you have a large number of water molecules. But you can't define the boiling temperature of a single molecule: it has no meaning, does it?

A given atom will react differently within different environments, giving different observable properties. So you need to look at the entire system without considering its constituents independently: look at a molecule as a whole without considering first the carbon atoms, then moving to hydrogen atoms,... It probably makes chemistry harder to predict, but also more interesting. 

[nojnoj]

atoms, It probably makes chemistry harder to predict, but also more interesting. 

I can see that, definitely. Chemistry has always been the black hole in my scientific knowledge, but now I'm (eventually) coming round to its charms. And that's only slightly because of Breaking Bad.

Another question, though: If you see an arbitrary set of, say, 2, 3 or 4 chemical elements which you're not familiar with - i.e you don't know their chemical behavior for sure - does long experience give you a kind of sixth sense in what to expect if they're reacted together?

In spite of knowing about chaos and quantum theory, I just can't get over wanting to see some kind of pattern and structure (and predictability) in the physical world!!