The element with the lowest atomic number is hydrogen, which has an atomic number of 1. It is the lightest and most abundant element in the universe.
On the other hand, the element with the highest atomic number currently known is oganesson, with an atomic number of 118. Oganesson is a synthetic element and belongs to the group of superheavy elements. It was first synthesized in 2002 and is highly unstable, with isotopes having extremely short half-lives. Due to its high atomic number and instability, oganesson is primarily a subject of scientific research, and its chemical properties are not well-known.