More than 102 Periodic Table elements

Question

Why isn't there more? Can we form more?

Answer 1

There are actually 117 at present, although 118 are shown on the Periodic Table. Elements 1-116 and 118 have been observed/synthesized; element 117 has not (at least, if it has, the discovery hasn't been announced yet.)

The reason why there are so few is that a nucleus of high atomic number has a large number of protons - which are all repelling each other. In lighter nuclei, the strong nuclear force does a good job holding together these protons against their electrostatic repulsion. However, in larger nuclei (those with more than 82 protons), the electromagnetic force wins out due to the large number of protons, and the nucleus, being unstable, decays. Understandably, the more protons there are, the more unstable the nucleus is, and the more quickly it will decay. The nucleus of element 118 decays with a half-life of about 1 millisecond.

We can probably synthesize nuclei of even higher atomic number, but they will be even more unstable, and unlikely to form as a result. We certainly won't be able to obtain macroscopic samples of transactinide elements, at least not unless we develop some amazing technology... also, if a nucleus had a charge greater than the reciprocal of the fine structure constant, it would decay much more quickly than lighter nuclei, due to electron-positron pair production.