Paradigms and paradoxes: the ionization potential of atomic astatine (Z =85), polonium (Z = 84), and some other elements—what does this value tell us about the energetics of atomic and diatomic halogens

The newly measured ionization potential of atomic astatine is discussed and compared with that the recently determined value for polonium other halogens. Regularities in these values are applied to understanding energetics diatomic Some surprises remain.