the element with the highest atomic weight is Oganesson (Og) with the atomic number 118. Its atomic weight is approximately 294 atomic mass units. Oganesson is a synthetic element and was first synthesized in 2002 by a team of Russian and American scientists. Due to its high atomic weight and unstable nature, Oganesson is a highly radioactive element and has a very short half-life. Please note that scientific discoveries and information can evolve over time, so it's always a good idea to consult the latest sources for the most up-to-date information.