Extended Periodic Table
There are currently seven periods in the periodic table of chemical elements, culminating with atomic number 118. If further elements with higher atomic numbers than this are discovered, they will be placed in additional periods, laid out (as with the existing periods) to illustrate periodically recurring trends in the properties of the elements concerned. Any additional periods are expected to contain a larger number of elements than the seventh period, as they are calculated to have an additional so-called g-block, containing 18 elements with partially filled g-orbitals in each period. An eight-period table containing this block was suggested by Glenn T. Seaborg in 1969.
No elements in this region have been synthesized or discovered in nature. The first element of the g-block may have atomic number 121, and thus would have the systematic name unbiunium. Elements in this region are likely to be highly unstable with respect to radioactive decay, and have extremely short half lives, although element 126 is hypothesized to be within an island of stability that is resistant to fission but not to alpha decay. It is not clear how many elements beyond the expected island of stability are physically possible, if period 8 is complete, or if there is a period 9.
According to the orbital approximation in quantum mechanical descriptions of atomic structure, the g-block would correspond to elements with partially filled g-orbitals. However, spin-orbit coupling effects reduce the validity of the orbital approximation substantially for elements of high atomic number.
Famous quotes containing the words extended, periodic and/or table:
“I have been accustomed to make excursions to the ponds within ten miles of Concord, but latterly I have extended my excursions to the seashore.”
—Henry David Thoreau (18171862)
“But parents can be understanding and accept the more difficult stages as necessary times of growth for the child. Parents can appreciate the fact that these phases are not easy for the child to live through either; rapid growth times are hard on a child. Perhaps its a small comfort to know that the harder-to-live-with stages do alternate with the calmer times,so parents can count on getting periodic breaks.”
—Saf Lerman (20th century)
“Will you greet your doom
As final; set him loaves and wine; knowing
The game is finished when he plays his ace,
And overturn the table and go into the next room?”
—Philip Larkin (19221986)