Superheavy elements

Made a few atoms at a time and gone in a flash: the elements at the very edge of the periodic table.

The last fifteen boxes of the periodic table hold elements that no one has ever seen. Not because they are hidden, but because they exist for such a short time and in such tiny numbers that a visible sample is impossible. Rutherfordium to oganesson, elements 104 to 118, are made by smashing lighter atoms together in particle accelerators, and most of the atoms created decay within seconds or fractions of a second.

They are sometimes called the transactinides, because they come after the actinides, or simply the superheavy elements. Their discovery completed the seventh row of the table. Whether an eighth row can be started is one of the open questions in nuclear science.

What they have in common

Every superheavy element is synthetic. None occurs in nature. To make one, scientists fire a beam of medium-weight nuclei, such as calcium, at a target of a heavy element, such as plutonium or californium, and hope that occasionally two nuclei fuse. The odds are terrible. Experiments can run for months and produce a handful of atoms, and each atom is identified only by the trail of radiation it leaves as it decays.

Because so few atoms exist for so little time, almost nothing about these elements has been measured in the ordinary way. Melting points, densities and colours are calculated from theory or estimated by extending trends from the elements above them.

Their names honour scientists such as Rutherford, Seaborg, Bohr, Meitner, Roentgen and Copernicus, and places such as Dubna, Darmstadt, Japan, Moscow, Livermore and Tennessee where the work was done.

How they change across the row

On paper the superheavy elements simply continue the seventh row. Rutherfordium to copernicium fill groups 4 to 12, so they should be transition metals like hafnium to mercury above them. Nihonium to oganesson fill groups 13 to 18, so they should run from a post-transition metal to a noble gas.

Reality may be more interesting. In atoms this heavy the innermost electrons orbit at a large fraction of the speed of light, and the effects predicted by Einstein's theory of relativity change the sizes and energies of the electron shells. The result is that the usual trends can bend or break. Copernicium and flerovium are predicted to be far more volatile than mercury and lead above them; the dataset gives copernicium a boiling point around 84 degrees Celsius and flerovium a melting point around 67 degrees, and some models suggest either could be a gas at room temperature. Oganesson, which should be a noble gas, is predicted to be a solid with a boiling point near 77 degrees Celsius.

Predicted densities climb to remarkable values in the middle of the row. Hassium is estimated in the dataset at more than forty times the density of water, which would make it the densest element of all if it could ever be gathered into a lump.

Where you meet them

You do not. No superheavy element has any practical use, and none ever will unless a far longer-lived isotope is found. Their value is entirely scientific. Each new element tests whether the patterns of the periodic table still hold at the extreme edge of the known elements.

The places you meet them are laboratories. A few research centres around the world have the accelerators and detectors needed for this work, including institutes in Russia, Germany, the United States and Japan whose names are written into the elements themselves. The single-atom chemistry experiments have produced some genuine results: hassium has been shown to form a volatile oxide like osmium above it, seaborgium and bohrium behave like their lighter group members, and copernicium and flerovium have been caught interacting weakly with gold surfaces in ways that hint at their odd predicted behaviour.

Odd ones out

Seaborgium and oganesson stand out for their names. Both honour scientists who were alive when the name was chosen, Glenn Seaborg and Yuri Oganessian, which was highly unusual. Oganesson is also the only element in this family whose expected behaviour contradicts its group so strongly: a noble gas that may not be a gas and may not be especially noble.

Rutherfordium and dubnium are the odd ones in a historical sense. Their discovery was disputed for decades between teams in different countries, and the argument over what to call them delayed the naming of the whole row. And beyond the row lies element 119, which appears in the dataset as a placeholder with the temporary name ununennium. It has not yet been confirmed. If it is made, it will open an eighth row of the periodic table and begin the story again.

The numbers

Melting points fall down the list, from Rutherfordium at 2127 °C to Tennessine at 450 °C.

Density in g/cm³ (g/L for gases). Values for synthetic elements are predictions.

Did you know?

• Every superheavy element is synthetic; none occurs in nature and none has a practical use.
• These elements are made by fusing two lighter nuclei in a particle accelerator, sometimes only a few atoms per year.
• Seaborgium and oganesson are the only elements named after people who were alive at the time of naming.
• Hassium is predicted to be the densest element of all, at more than forty times the density of water.
• Oganesson completes the seventh row of the periodic table and is predicted to be a solid, not a gas.
• Element 119, provisionally called ununennium, has not yet been confirmed to exist.

Frequently asked questions

Written by Anthony. Data from Periodic-Table-JSON (CC BY-SA).