highatomicnumber

High atomic number refers to elements with a large number of protons in the nucleus, quantified by the atomic number Z. In practice, this term is often applied to the superheavy elements, with Z well above the naturally occurring elements, typically Z greater than 100. Most high-Z elements have no stable isotopes and are radioactive.

Elements with Z greater than 92 have no stable isotopes, and most with Z greater than 100 are synthetic. They are produced in specialized facilities by colliding nuclei in particle accelerators or, for some, by neutron capture in reactors. Production yields are extremely small, and the resulting atoms exist only briefly before decaying.

As Z increases, the Coulomb repulsion between protons grows, making very large nuclei increasingly unstable. Nuclear models predict that a region termed the island of stability may exist at certain combinations of proton and neutron numbers (often cited near Z ≈ 114–126 and N ≈ 184), where some isotopes could have relatively longer lifetimes compared with neighboring nuclides.

Relativistic effects also become important for high-Z atoms, altering electron energies and orbital shapes. These effects can cause departures from simple periodic trends and lead to unusual chemical behavior, but the chemistry of many high-Z elements remains poorly understood because of their short lifetimes and the difficulty of production.

Research into high atomic number elements tests theories of nuclear structure and relativistic quantum chemistry, informs the limits of the periodic table, and guides efforts to discover longer-lived superheavy nuclei.