Chris Groat on mon 26 feb 07
In gen. chem. we were taught about two types of bonds; ionic and covalent.
Eventually we learned that these two types of bonds are just ideals. Most
bonds are a combination of the two. e.g. coordinate covalent bonds. It's
when a lewis base donates a pair of free electrons to a lewis acid to form
a coordination complex. Copper is an atom that likes to form coordination
complexes. I'll have to check back with my college texts, but I believe
certain oxidation states give way to coordination complexes with different
geometries. Perhaps copper's oxidation state of +1 gives way to a
coordination complex geometry that is less stable?
Chris
Ivor and Olive Lewis on tue 27 feb 07
<copper?>>
Dear Dave,
In answer to your question I have come to the conclusion that it is the =
type known as "Coordinate Covalent Bonding"
This is rather complex and my argument that leads to that conclusion is =
based on knowing about electronic structures of atoms and how they can =
behave. Our ability to cause the retention of Copper Ions may depend on =
our ability to control the availability of Oxygen ions. This in turn may =
be governed in part by the M2O/MO/MO2 ratio or our ability to increase =
the number of NBO's, which would have the consequence of lowering the =
maturity point of Copper rich glaze.
But remember, I may be way of beam and this could be an impossibility.
Thanks for your thoughts.
Best regards,
Ivor
Megamelon on wed 28 feb 07
Na and K are almost always soluble ions (extremely few exceptions... I =
remeber because I taught in in grad school...). If a K or Na ion sits =
in a lattice deep enough, then it may be stabilized merely because it's =
inaccessible because of interfering glass matrix. This could loosely be =
termed a "steric effect". If water cannot access something, then it =
will not dissolve into water. Doesn't matter if it's ionic or covalent =
bonded there- if it's encased in glass, then water doesn't get to it, =
and it won't sublime.
Now- loose ions on the outside monolayer would, of course, be =
susceptible, but that won't have a big effect on the bulk substance. =
Even if there are pores in the material- some solution has to be able to =
migrate in, dissolve the ionic species, and it must be able to fit back =
out in hydrated form (much larger than a bare ion). Another case of =
steric hindrance.
Same principle used in molecular sieve material etc.
Yes, I am a chemist geek.
-pH
Paul Haigh
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