Period 2 element Period 2 element A period 2 element is one of the chemical elements in the second row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behavior of the elements as their atomic number increases; a new row is started when chemical behavior begins to repeat, creating columns of elements with similar properties. The second period contains the elements lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, and neon. This situation can be explained by modern theories of atomic structure. In a quantum mechanical
Extended periodic table momentarily give an effective "Z" of 174; uranium with uranium gives effective "Z" = 184 and uranium with californium gives effective "Z" = 190). Supercritical atoms are hence expected to pose no difficulties with their electronic structure, so that the end of the periodic table may be determined instead by nuclear instability rather than electron shell instabilities. The stability of nuclei decreases greatly with the increase in atomic number after plutonium, the heaviest primordial element, so that all isotopes with an atomic number above 101 decay radioactively with a half-life under a day, with an exception of dubnium-268. No elements