the highest atomic number that has been officially confirmed and named is 118, which corresponds to the element Oganesson (symbol Og). Oganesson is a synthetic element that was first synthesized in 2002 by a team of Russian and American scientists. It is highly unstable and has a very short half-life.
Please note that the field of superheavy element research is ongoing, and new elements beyond atomic number 118 may be discovered and confirmed in the future. However, as of now, 118 is the highest atomic number on the periodic table.