11ya inert pair is a reason too..BiF5 exists cause F is electroneg. enough to cause the d-orbital contraction...Cl is not electroneg enough to do so...saw it in J.D LEE.
3 Answers
1Dude , Bi+5 state is very unstable due to high charge on a large atom . this normally splits into
Bi+3 ion. though very less no. of compounds exist, having Bi+5 state i.e. BiF5 , Bi2O5
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