Can't nobelium form compounds like other lanthanides/actinides do?
Wikipedia reports that nobelium does form compounds, but unlike other later actinides it could adopt a +2 oxidation state as well as +3, which complicates identifying specific compounds (e.g. nobelium reacts with chlorine but the specific product is not known).  The +2 state is stabilized by the full shell configuration $[\ce{Rn}]5f^{14}$.  Experiments in aqueous solution seem to show a preference for the +2 oxidation state, and $\ce{No}^{2+}$ has been coprecipitated into solids.  But we have yet to definitively identify a neat nobelium compound in either specific oxidation state.