why are pentahalides more covalent than trihalides?

 

Covalent bonds are formed as a result of sharing of electrons between two elements.

In a pentahalide 5 electrons are shared between the two elements whereas, in a trihalide 3 electrons are shared. The higher the number of shared electrons the more covalent the bond becomes.

Therefore, pentahalides are more covalent in nature as compared to trihalides.