Xenon

An element. To be more precise, it is a noble gas, meaning its outermost shell of electrons is packed with 8 valence electrons. The best of the noble gases, without question, and the second best element, besides Yttrium. Xenon is so cool and unreactive (nonchalant), that high school sophomores use it in electron configurations, for god knows what reason. It's lowkey heavy, with an average weight of 131 AMUs.