[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??

[FeLiXe]

first there is no clear distinction between ionic and network covalent, but it's rather gradual. the clear question is if a given compound is a molecule or crystal
and I don't think electronegativity is so important for determining that.
i guess eventually it's experience and there are some rules. for example the transition metal halides are often molecules, the oxides crystals, the reason is that bivalent oxygen can easily create a network even if the substance is not totally ionic.