Shirley McQueen, of Dunedin, asks :-

At the bottom of the Periodic Table there are elements listed starting with the letters Un. What are these?

John Campbell, a physicist at the University of Canterbury and author of the book "Rutherford Scientist Supreme" and producer of the documentary "Rutherford", responded.

They are heavy elements of atomic number greater than 100 that have been produced in nuclear reactions but not yet named, or not yet produced.

This uniform naming system was set up in 1978 by the International Union of Pure and Applied Chemistry (IUPAC) to avoid confusion. The three letters are the first letters of the relevant latin numeral roots. The first two for elements 100-109 are based on un (=1) and nil (=0) so all start with Un. Predicted element 100 was Unn, 101 Unu, 103 Unt (t=tri), and 104 Unq (q = quad). 118 is ununoctinium (Uuo with o = octo)

Once a new element has claimed to have been produced its production must be confirmed by other groups and then the discoverer is formally invited to give it a name. For example, after Albert Ghiorso and co-workers at the Lawrence Berkeley Laboratory of the University of California spent a year attempting to repeat the work of a Russian group who claimed to have produced element 104 (or Unnilquadlium or Unq for short) but this remained unverified. In 1968 the Berkeley team produced element 104 by bombarding the world's supply of californium (element 98) with high speed nuclei of carbon atoms.

In November of 1969, at celebrations marking the centennial of Mendeleev's periodic table, Al Ghiorso proposed that element 104 be named rutherfordium (Rf) because Ernest Rutherford was one of his heroes. After a lot of horse trading on names from other groups concerning different elements, element 104 is the only element named after a New Zealander. This was rather fitting as Rutherford was the first to explain radioactivity by demonstrating that some heavy elements decayed (transmuted) naturally into slightly lighter ones, discovered the alpha particle and the proton, introduced the concept of half-life (the time taken for a number of identical atoms to radioactively decay to half of their initial number), invented the Rutherford-Geiger tube (nowadays the Geiger-Muller counter) to detect individual ionizing particles, proposed that the neutron had to exist, and directed the team that produced the first particle accelerator to allow new isotopes to be produced entirely artificially.

As of 2016 the periodic table consists of confirmed elements up to 118. About three groups in the world currently have heavy ion accelerators and are pushing upwards because there are theories that some elements at about 126 might be stable elements.