JOIN USThere are 92 naturally occurring elements from Hydrogen to Uranium, constituting the classic periodic table. Heavier elements beyond Uranium continue to be discovered, writes C Sivaram.New transuranium elements beyond Uranium, the highest atomic number element occurring in nature continue to be discovered.
From Hydrogen to Uranium, there are 92 naturally occurring elements. These constitute the classic periodic table. The heavier elements beyond Uranium are all unstable and their longest living isotopes have lifetimes much smaller than the age of the earth, i.e. four-and-a -half billion years.
Neutrons released copiously in the fission of the U-235 isotope (in reactors) first led to the production of transuranium elements like Neptunium and Plutonium. Plutonium also has fissionable isotopes like Pu-240, which provides fuel in breeder reactors producing Plutonium from Uranium. Uranium was named by Klaproth who discovered it, after the planet Uranus, the latest addition to the solar system at that time!
So it was natural to name Neptunium after Neptune and Plutonium after Pluto, discovered in 1930. Earlier, Cerium, a rare earth, was named after minor planet Ceres, discovered in 1801, Helium after the sun, Selenium after the moon and Tellurium after the earth.
Not all lower atomic number elements in the periodic table are stable. For instance, there are no stable isotopes of the elements Technetium and Promethium. Technetium, the name coming from Greek for “artificial” was indeed made in reactors, its longest isotope living only for a few lakh years.
Interestingly it was later identified in a peculiar category of carbon stars, in astronomy. This proved that the synthesis of rare elements is also occurring continuously by nuclear reactions in these stars. Promethium, also identified later in stellar sites, also does not occur naturally on earth and is named after the Greek Titan Prometheus who was punished by the Gods for bringing fire to the earth.
Naming tradition
Plutonium was followed by the production of element Americium, named after America, which became element 97. There is another much lower atomic number Ruthenium named after Russia. However, Indium is not named after India but after the bright indigo lines of the element spectrum!
The rare earth Europium is named after Europe. No other elements are named after countries or continents, but there are a couple of elements, mainly rare-earths, named after cities, like Lutetium from Lutetia for Paris, Holmium (after Copenhagen) and Hafnium. Although earlier very few elements were named after individuals, like Gadolimium that is used in nuclear control rods, named after Col.
Godolin, most of the transuranium elements, especially those identified recently are named after eminent scientists. The trend started with naming no 96 after Curie as Curium, then Einsteinium.
Ironically Einsteinium was a byproduct in an H-bomb explosion. Then we had Fermium, Mendelevium, after Mendeleev, the discoverer of the periodic table, Nobelium, named after Alfred Nobel, and Lawrencium, after the cyclotron inventor E O Lawrence. There are also elements named after Rutherford, Niels Bohr, Otto Hahn, Lise Meitner and very recently element No 111, earlier called Unununium has been named Roentgenium after the discovery of X-rays and element No.112 is named after the astronomer Copernicus who revolutionised astronomy with his heliocentric theory.
Studying super heavy elements
The properties of the unnamed element with atomic number 113 are right now being studied. These fragile super heavy elements are sometimes dubbed SHEs.
They are not found in nature and most of those made in laboratories decay almost immediately. For instance, element 113 decays in milliseconds and its official entry into the periodic table is a long-drawn process. One has to be very careful before being certain that a new element has been produced. It is to be recalled that earlier published reports of elements 116, 118, etc were withdrawn.
The production of these elements is complex and very little is produced. Only about 30 atoms of element 113 are made a year. It is formed when charged ions of calcium collide with berkelium nuclei. This produces a nucleus of atomic no.117 which alpha decays to form 113.
An important goal is to study the properties of the SHEs, some of which might have exotic properties that could be used by incorporating them in new materials. Element 113 has a closest cousin or homologue just below it on the periodic table. This is Thallium. As is well known, in the periodic table, elements which differ in atomic number by 8, 18 or 32 have similar properties.
So Copernicium should have analogous properties to Mercury, the only metal which is a liquid at room temperature. The element Gallium will melt in your hand (melting point around 30 deg. Celsius). To study the properties of the few atoms of the SHEs available, the atoms would be raced through a tube and fired across a sheet of gold.
How far the atoms travel across the gold surface would measure their reactivity which in turn tells how tough it would be to break them apart and form a gas. Comparing this with the distance traversed by their homologues would enable their properties to be compared.
This technique has now shown the latest addition to the periodic table that is Copernicium (element 112) is more volatile than its homologue Mercury and so becomes the only metal known to be a gas at room temperature.
Transuranic chemistry is likely to yield many surprises with many exotic elements waiting to be discovered.