Question of the Week, 7.6.2011
There are currently seven periods in the periodic table of chemical elements. The last known element has an atomic number 118. The question is whether there is the eight or even others periods. It’s clear that elements from these periods will be extremely unstable. However, for example the element 126 is hypothesized to be within an island of stability that is resistant to fission (but not to alpha decay).
Classical Bohr model fails for elements with an atomic number greater than 137 as the speed of core electrons would exceed the limit of speed of light. Richard Feynman also predicted this element (sometimes called Feynmanium) to be the last possible, as further there wouldn’t be an energy gap between positive and negative energy states. More realistic predictions which take into account the finite extension of the nuclear-charge distribution predicts the critical Z of about 173.
Further reading:
http://en.wikipedia.org/wiki/Extension_of_the_periodic_table_beyond_the_seventh_period
Libor Veis