An interesting element of the periodic table - one that has never actually been observed - is element 137, which has an atomic number that exceeds the highest known naturally occurring element in the periodic table, plutonium, (element 94) by 43 protons, and is known as Untriseptium, or as the Wikipedia reference on this remarkable element notes, is sometimes called Feynmanium.
The reason that an element that has not been discovered - and thus has no formal IUPAC name - has been named "Feynmanium" by people who think about this element - is that the famous physicist (and iconoclast) Richard Feynman noted that the atomic charge on the nucleus of untriseptium was such that the electrons in it would need to travel almost as fast as the speed of light, faster than the speed of light for any heavier element, according to a widely used partial differential equation known as the Relativistic Dirac Equation, and in fact, according to the highly successful (if necessarily approximate) Bohr model of the atom.
According to the Bohr interpretation, the speed of an electron in the innermost shell is approximately equal to the atomic number of an element, commonly denoted as Z, times the speed of light, commonly denoted c, and a parameter, α, which is a fundemental constant of the universe, the fine structure constant, itself equal to the charge on an electron squared times the speed of light, times the permeability of free space (the magnetic constant), divided by twice Planck's constant.
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