IrC - 6-2-2006 at 00:40
I have a truckload of good chemistry books, but they all seem useless on a few points. How do you predict which valence a variable valency element
will have ahead of time? Iron III Chloride or II for example, somewhere I remember that having enough chlorine to give three to each is desired but
why would not many of the molecules be the other valence leaving chlorine left over? Assuming a product falls out of solution for example, leaving
unreacted elements, why would not the lower valence compound be unaffected simply because there was an excess of say chlorine left over? Is it just a
statistical probability that the II molecule being in contact with excess reactant would again react and grab another atom, as in the chlorine
example? Could you make it all one or the other by stopping the reaction short? Also how do you tell from electronegativities exactly what chemicals
do what in a reaction?
12AX7 - 6-2-2006 at 07:48
I don't think propability really comes into this, atoms are usually ionized to a definite amount and tend to stay that way until something acts on
them (i.e. oxidizer or reducer). That is, you should be able to add one isotope mixture of Fe(II) to a solution of Fe(III) with a different isotopic
ratio, mix them, then seperate (mind you without air, which would oxidize Fe(II)) and you should get the same isotopic mixtures you started with.
sparkgap - 6-2-2006 at 07:55
I'm quite hazy on my transition metal chemistry, but IIRC, hydration is a factor in what valence would a particular metal take. Something about the
metals trying to have their d-shells either half or fully filled 'cause they're more stable that way and water helping in the electron placement. 
sparky (^_^)
unionised - 6-2-2006 at 13:09
I'm pretty sure that the Fe(III) / Fe(II) isotopes would scramble. There are tables containing the electrode potentials for that couple and the Nernst
equation says how that potential varies with the ratio (III)/(II). For these values to be well defined the species have to be at equilibrium so the
reaction must be reversible.