# Are there unknown elements our periodic table is missing?

Feb 20, 2016

If there are, then they are at the end of the periodic table.

How far does your copy of the periodic table go?

#### Explanation:

The atomic number is the number of protons in the nucleus of an atom of an element. As such, it is a positive integer starting with $1$ for Hydrogen then up to $118$ for Ununoctium (a.k.a. eka-radon). Only a few atoms of Ununoctium have been synthesized and detected.

Elements $119$ (Ununennium or eka-francium) and $120$ (Unbinilium or eka-radium) are hypothesised and various attempts are being made to synthesize them. Their predicted lifetimes are very short.

Footnote

In 1959, when the heaviest known element was Nobelium (atomic number $102$) Tom Lehrer wrote a song "The Elements" (to the tune of "A Modern Major General") naming all of them. It ends with a typically Lehrer style rhyme: "These are the only ones of which the news has come to Harvard, and there may be many others but they have not been discovered" (pronounced "dis-car-vard").