there is no known upper limit to the atomic number of radioactive elements. Radioactive elements can have extremely high atomic numbers, and the periodic table is theorized to extend beyond the elements we have discovered so far.
Elements with high atomic numbers beyond what is naturally occurring on Earth are typically referred to as transuranium elements or superheavy elements. These elements are created synthetically through nuclear reactions in laboratories and have short half-lives, making them highly unstable and radioactive.
The discovery and synthesis of superheavy elements have been a subject of ongoing scientific research. Elements with atomic numbers up to 118 have been officially recognized by the International Union of Pure and Applied Chemistry (IUPAC) as of 2023, with element 118 being oganesson (Og). However, scientists continue to search for and attempt to create even heavier elements.
It is worth noting that as technology advances and our understanding of nuclear physics improves, it is possible that researchers may discover or synthesize elements with even higher atomic numbers in the future.