Ionization

[Paulhoff]

http://en.wikipedia.org/wiki/Ionosphere

Yes, the ionoshere, a good part of what Amateur Radio is all about.

Paul

 

[anor277]

I Repeat:
In my defense- when I told you that dissolving a salt is a physical (not chemical) process, if you had any scientific sophistication you would have done a Homer Simpson: D'oh. Failing that- you are beyond my help, here. And, I have no plans to teach introductory chemistry any time in the near future.

You may, arguably, argue on ...

Of course I may argue on and on. You have not defined your terms, you have not advanced any evidence in support of your position, you persist in ad homs. Again, please respond to the argument if you wish to continue.

 

[anor277]

It's referred to as a bond in introductory chemistry, but seldom after that.

So you accept my premise but equivocate. And it was claimed (not by you) that I was the one who needed to revise my introductory chemistry. Doesn't introductory chemistry apply later on as well?

But you could say the same thing about hydrogen bonds, and nobody would say that dissolving sugar in water, or boiling ethanol are chemical changes.

And I haven't claimed that dissolving sugar in water or boiling ethanol are examples of chemical change. No bonds are broken (except H-bonds), and no new substances are formed.

Take an ionic compound like copper(II) sulphate pentahydrate. If you dissolve it in water, you're not hydrating the copper ions or the sulphate ions much more than they were in the solid form (the copper stays as [Cu(H2O)4]2+, and the sulphate has one water attached to it in the solid form). Do you consider this to be a chemical change? If not, how is this so different from dissolving an unhydrated salt?

Well, at least now were in the area of coordination chemistry, an area where chemical change, by exchange of ligands at the metal centre, is a well-established phenomenon. I will confine myself to discussion of the coordination environment around the metal centre. In solution the copper ions probably exists as the hexaaqua complex, [Cu(OH₂)₆]²⁺. If in the solid state, if the sulfate anion acted as a sulfato ligand, i.e. pentaquasulfatocopper(II) (and I don't know the solid state structure of that salt offhand), then chemical change has indeed taken place, i.e. solid, 5 oxo, and one sulfur donors, solution 6 oxo donors - the technical term for this process is coordination isomerism and I doubt you'll maintain that isomerization is a physical process. For NaCl the case for chemical change is even more compelling. In the solid, the metal ion is 6-coordinate and has 6 chloride anions as nearest neighbours; in solution, it has 6 water molecules as nearest neighbours. Bonds have been broken and new substances formed - manifestly chemical change.

The whole argument is unnecessary, really. If I'm teaching my students the difference between physical and chemical changes, I'll call dissolution (of covalent or ionic compounds) a physical change. If I'm doing equilibrium or thermodynamics, I treat chemical and physical changes the same anyway.

And if dissolution involves the breaking of chemical bonds and the formation of new substances, I would tell my students that it is an example of chemical not physical change.