Question: why clf3 is not a trigonal planar?
Answer: Why is a molecule like ClF3 T-shaped and not Trigonal Planar? In a lone pair (lp), the average position of the electrons is closer to the central atom than the electrons involved in a covalent (in this case Cl-F) bond, so they have a slightly greater repulsion to other lone pairs (or bonds), than a bond does.