Metrium

Metrium is the $$8.644 \times 10^{51}$$th element, which makes the atom exactly 1 meter in diameter.

At this point in the periodic table, individual elements have stopped being named, since there would be too many to list. Currently, there are 5,813,547 named elements, majority of which are special in one way or another.

Metrium has been only speculated to exist for the longest time, until the only known Metaperiodicverse was found, consisting of Multiperiodicverses, which in turn, contained every Periodicverse, according to all laws in the domain of the Metaverse. This allowed for thorough explorations to be done on each Periodicverse to discover as many elements as possible.