Chapter 6, Problem 81QRT

Tribromide, ${\text{Br}}_3^{-}$, and triiodide, ${\text{I}}_3^{-}$, ions are often found in aqueous solutions, but trifluoride ion, ${\text{F}}_3^{-}$, is so rare that its bond strength was only measured in 2000. Explain.