Question

Why do some noble gases form compounds with fluorine and oxygen only ?

Answer 1

The story starts with a gentleman name Neil Bartlett, in 1962 he tried to oxidize molecular oxygen with platinumhexa flouride and observed following result

O2 + PtF6   = O2PtF6

Thus molecular oxygen converts to O2+ 

Ionisation Energy of  molecular oxygen is 1165 kj/mole whereas ionisation Energy of Xe was observed as 1170 kj/mole 

Due to nearly same ionisation energies of O2 and Xe , he thought that similar compound can be given with Xe and prepared first compound of Noble gas XePtF6

Now answer of your question

Some Noble gases (Xe and Kr)  form compounds because of their comparatively lower ionisation energies....