The rare radioactive substance made its way from the United States to Russia on a commercial flight in June 2009. Customs officers balked at accepting the package, which was ensconced in lead ...

For now, they're known by working names, like ununseptium and ununtrium — two of the four new chemical elements whose discovery has been officially verified. The elements with atomic numbers 113, 115, ...

The heaviest element that humans have ever found is called oganesson. Each atom of the stuff packs a whopping 118 protons into its dense center. In contrast, hydrogen—the most abundant element in the ...