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 of the recently determined value for polonium and for the other atomic halogens. Regularities in these atomic values are discussed and applied to the understanding of the energetics of diatomic halogens. Some surprises remain.