Scientists are pushing the edges of the periodic table more everyday.
If you’ve ever taken a close look at the periodic table, you’ve probably noticed the peculiar elements nearer the bottom that aren’t often talked about. No doubt you have heard more about sodium than about moscovium or roentgenium.
The term superheavy elements is used to refer to the heaviest elements in the periodic table. There is no exact definition of the term but generally it refers to elements with an atomic number greater than either 92 or 103.
In this part of the periodic table instability reigns, with many of the elements barely existing for a few milliseconds before falling apart into smaller, more stable species.
Fundamental structures
Atoms are composed of a nucleus in the middle – containing protons and neutrons – surrounded by a cloud of electrons. The positively charged protons are balanced out by the negatively charged electrons.
As you go down and across the periodic table, elements become larger and take on more protons, neutrons and electrons. They also grow more unstable as the internal interactions between the protons in the nucleus start forcing the atom apart.
To become more stable, heavy elements eject parts of themselves (becoming a lighter element) through a process known as decay. Atoms can also tear themselves apart through a process known as nuclear fission. The heaviest elements on the periodic table usually only last a fraction of a second before completely falling apart.
Atomic forges
Larger elements are created by forging two smaller elements together. This process usually requires an enormous amount of energy to overcome the natural forces pushing atoms apart. The 3 main ways this happens in nature are through Big Bang nucleosynthesis (the dawn of the Universe), stellar nucleosynthesis (in stars) and in supernova.
Superheavy elements do not occur naturally. So, to explore the edges of the periodic table, scientists are forced to create the elements here on Earth.
To do this, we utilise particle beams. These are beams of smaller particles accelerated to about 10% of the speed of light that are fired at a large nucleus or “target nucleus” to combine them. The speed is just enough to overcome the forces produced by the nuclei. Usually, it breaks the nucleus apart but occasionally it fuses to form a new element.
The newly formed atom exists for too short a time to detect it directly. To prove its existence, scientists instead measure the characteristic radiation given off by the atom and infer its existence from that.
Pushing the edges of chemistry
As we’ve become more familiar with superheavy elements, the scientific community has become increasingly curious about their properties.
Their limited lifespans mean that very little is known about them – we can’t explore their reactivities or compounds in conventional ways because they fall apart so quickly.
One way to characterise them is by accelerating the atom across a gold or quartz surface. It readily attaches to the surface depending on its chemical properties and its location can be found by measuring where the decay emits from. This gives us insights into how easily the superheavy element can bond and allows some rudimentary insights into its electron structure.
Scientists have done this with element 114, flerovium, where they found it has similar bonding properties to lead.
Some researchers hope to eventually find the “island of stability”, a predicted set of superheavy elements that are notably more stable than normal due to possessing a ‘magic number’ of protons and neutrons. Currently, the technology isn’t there yet to properly explore the island, but teams across the world are racing to prove its existence.