[penjuin]

I have always wondered this, but have never been able to find a clear explanation. I asked a friend who is studying chemistry at a higher level and was told to "look up electronegativity". I wikipedia'ed it, but it still leaves me confused.

When a burning match is placed in a CO2 environment it goes out, yet when burning magnesium is placed in a CO2 environment it just "steals" the oxygen. Is there any numerical (or algebraic) way to work out how much one ion wants another?

[Borek]

That's not easy - I would say that's what the whole chemistry is about

It is not just about "which ion likes which ion", it is about many concurrent competing processes. Process that leads to the lowest final energy of products wins (unless it is too slow, and other faster processes will win). In the particular case of magnesium in CO₂ strong ionic forces in the solid magnesium oxide are driving reaction in this direction.

[penjuin]

Thanks Borek, but could you please enlighten me as to the ionic forces that come in to play in my example? If nothing other then a starting point for me to continue to learn about them.

[Borek]

CO₂ is not ionic, it is covalent. MgO is ionic. In MgO crystall there are Mg²⁺ and O^2- ions - both relatively small and with relatively high charge. That mean they are strongly bond together, which further makes MgO preferred product in many reactions (but not all).

These things are best described not in terms of what happens at molecular level (although that's where the action is) but using theromodynamic functions:

http://en.wikipedia.org/wiki/Thermodynamic_potential
http://en.wikipedia.org/wiki/Gibbs_free_energy

unfortunately, thermodynamics is not easy to describe in laymans terms. Perhaps someone will be able to post better links.

[Arkcon]

It's hard for a layman to understand the background of the activity series, and thermodynamic potential and Gibbs Free Energy, one you understand them, will help a lot.  For a layman, there is some way of visualizing the activity series -- in our world, wood is common, you see it lying around all the time, you know likewise, that carbon dioxide means death to living things that require oxygen.  Yet, with a small amount of activation energy, wood will burn in the atmosphere.  Now take magnesium, yes, you'll find a block of it around from time to time, but you never find free elemental magnesium in an ore seam, as distinct from gold, platinum, often silver, rarely copper, even more occasionally iron.