[mountain23john]

Hello guys,
 I'm trying to figure out what kind of bonding is involved with Cr2O3. I know that when Cr has a +2 o.s. it tends to be ionic, and when Cr has a +4 O.s. it tends to be covalent. but what kind bonding is involved when Cr has a +3 O.s.?

My other question is If your given a transition metal oxide or a transition metal halide how do you predict the bonding? I know you can use electronegativitiy values but my teacher tells us those can be misleading. I also know that if you have really high o.s states the cmpds will tend to be covalent. what else can you use determine if the cmpd is ionic, molecular covalent or network covalent? Like CoO Co has a plus two o.s. but the e.n values predict it to be covalent??

i posted this somewhere else but it probly belongs here.

[Rabn]

Electronegativity values are misleading for transition metals becuase they exist in mltiple oxidation states, you would need to know the electronegativity for each oxidation state.  As far as I can see there is onle one likely way this bonds up since each Cr needs to "lose" 3 electrons:

O=Cr-O-Cr=O

As far as how to predict the bonding...http://en.wikipedia.org/wiki/Lewis_structure in case you need a refresher. Otherwise you can generally....generally assume that anything with a charge greater than plus 2 is not going to exist as an ion in very high amounts in aqueous solution, some polyprotic acids will, the solvent stabilizes the +3 ion. why won't water stabilize a transition metal but will a polyprotic acid? The acid interacts with water through hydrogen bonds, the transition metal cannot and is more likely to provide some oxidizing power.