The expanding periodic table

Our latest Friday science feature looks at copernicium — the latest addition to the periodic table of elements — with the help of Dr Paul Elliott, Lecturer in Chemistry at the University of Huddersfield

THE periodic table of elements, that famous chart on the bedroom wall of every chemistry student, is about to receive a new element.

Element 112 has been named copernicium (with the symbol Cp) by its discoverers, Professor Sigurd Hofmann and his team at the Centre for Heavy Ion Research in Germany.

So how do you get an element named after you? Well, first you have to have died — a new element can not be named after a living person. Second, you have to have made a great contribution to science. Copernicium has been named after the 16th century Polish priest and astronomer, Nicolaus Copernicus.

Copernicus is credited with formulating the heliocentric model. Before this, it was believed the Earth was the centre of the universe, about which all things revolved — the geocentric (Earth centred) model.

Copernicus’s model placed the Sun at the centre — heliocentric (Sun centred) — with all the planets, including Earth, orbiting it.

The model dramatically changed the accepted view of our place in the universe and was a major step forward in the development of science.

But back to the periodic table… what does it represent, what are the elements and where do they come from?

Chemists had known for a long time that many of the substances in the world could be made from or reduced to simpler materials. But there were some materials that could not be simplified further or made from combining other materials. These are the elements, the chemical building blocks of nature.

Other chemists, such as John Dalton, had provided extremely strong evidence that all substances were ultimately made of small particles we call atoms which combine to form molecules.

Based on these concepts, scientists were able to derive the relative weights of the atoms of different elements. This scale of masses for the different atoms of the different elements led to the formulation of the periodic table.

Russian chemist Dmitri Mendelev (who has his own element named after him, element 101, mendelevium) is widely regarded as the father of the periodic table.

By ordering the elements by atomic weight he noticed repeating patterns in their properties emerge.

The modern periodic table has atomic weight increasing from left to right with elements that show similar chemical behaviour grouped in columns. By constructing such a table, Mendelev noticed gaps and was able to predict both the existence and chemical properties of elements that were then later discovered.

But what are the atoms themselves made of?

These mysteries were unravelled by early 20th century scientists who identified the existence of the smaller particles from which atoms are made; positively charged protons and neutral neutrons (which together form the small atomic nucleus and provide the vast majority of the atoms weight) and tiny negatively charged electrons (which orbit around the atomic nucleus).

The element number is simply the unique number of protons in the nuclei of the atoms of a given element.

After the big bang, the main constituent of the universe was almost entirely hydrogen, whose atoms contain a nucleus containing a single proton. As this hydrogen condensed under its own gravitational attraction, stars formed and in the intense pressure within them, nuclear reactions occurred in which atoms squash together and merge to form heavier atoms of new elements.

This process, nuclear fusion, gives out energy and is why the Sun and other stars shine.

This process is able to make elements all the way up to iron (element 26). Any element heavier requires energy to be put in and was formed in the supernova explosions that marked the deaths of these first stars. Our Sun, the Earth and other planets, formed from the elements in this cosmic debris.

There are about 90 naturally- occurring elements, the remainder are man made. Nuclear reactors can be used to create elements up to fermium (element 100). Higher “super heavy” elements require the use of atom smashing particle accelerators.

Results have been published demonstrating that atoms of elements up to number 118 have been made. However, many experiments have to be carried out, taking many years, in order to confirm the findings before the International Union of Pure and Applied Chemistry (IUPAC) will accept a new element and add it to the table.

To make copernicium atoms, Hofmann and his team used a particle accelerator to fire atoms of zinc into a target of lead atoms.

As the zinc atoms smash into the lead atoms, their nuclei merge to create the nucleus of the new element. In common with all the other super heavy elements, copernicium nuclei are highly unstable and only have a lifetime of a few milliseconds to seconds before decaying and breaking up.

One of the aims of this type of research is to reach the fabled island of stability, a set of super heavy elements with particular numbers of protons and neutrons that are predicted by calculations to be much more stable with much longer lifetimes.

Hofmann is already attempting to make atoms of element 120 and so it may not be long before his voyage through the so-called sea of instability sights land and the periodic table gets even bigger.