question_answer

\[Cl{{F}_{3}}\] exists but \[FC{{l}_{3}}\] does not. Why?

Answer:

                Chlorine has vacant 3d-orbitals and an electron can be promoted from 3p filled orbital to 3d orbital. Thus, chlorine can show a covalency of 3 in its compounds and a molecule of \[Cl{{F}_{3}}\] can exist. But fluorine has no vacant Id orbitals and can exhibit only covalency of one in its compounds. Thus, a molecule of \[FC{{l}_{3}}\] fails to exist.