The periodic table consists of about 90 elements that occur naturally ending with element 92 uranium. This lack of precision is deliberate since one or two elements such as technetium were first created artificially and only later found to occur naturally on earth. This kind of occurrence provides a foreshadowing of things to come when we begin to discuss the transuranium elements, meaning those beyond uranium that have been artificially synthesized. Chemists and physicists have succeeded in synthesizing some of the elements that were missing between hydrogen (1) and uranium (92). In addition, they have synthesized a further 25, or so, new elements beyond uranium, although, again, one or two of these elements, like neptunium and plutonium, were later found to exist naturally in exceedingly small amounts. The existence of superheavy elements raises a number of interesting questions that pertain to the field of philosophy of science and also sociology of science. In fact, the very question of whether these superheavy elements actually exist needs to be dissected further, as it will be in the course of this chapter. The synthetic elements are extremely unstable, and only the lightest ones among them have been created in amounts large enough to be observed. Roughly speaking, the heavier the atom, the shorter its lifetime is. For example, the heaviest element for which there is now conclusive evidence is element 118, a few atoms of which have been created in just one single isotope form and with a half-life of less than a millisecond. Laypersons and specialists alike have asked themselves in what sense these elements can really be said to exist. The superheavy elements also have philosophical implications for the study of the periodic system as a whole and the question of whether there is a natural end to chemical periodicity. A related question, which has now become quite pressing, is the possible extension of the periodic table to include a new g-block which in formal terms should begin at element 121.
