Lead

Approaches to element 120 (unbinilium)

Attempts have been made at GSI to make element 120 (unbinilium). Several new elements have been made at GSI in the last few years. However after 120 days no decay chain of element 120 was found. With the total number of 2.6 × 1019 projectiles which impinged upon the target, it deduced that the stability in the region around Z=120, N=184 is not exceptionally high with respect to the neighbouring regions.

Currently it is not clear what proton number defines the location of the "island of stability". Various theoretical models suggest numbers of Z=114, 120 or 126. Workers at GSI investigated the element Z=120 (element 120, containing 120 protons within the nucleus). Three different projectile-target combinations all lead to the same compound nucleus 302120 or 302Ubn

  • 64Ni + 238U
  • 58Fe + 244Pu, and
  • 54Cr + 248Cm

The neutron number of the compound nucleus 302120 is N=182. This is only 2 neutrons below N=184 where the neutron shell closure is expected. Therefore, 302120 or 302Ubn is closer to the N=184 shell than any other so far produced compound nucleus with lower Z.

The largest production rate for Z=120 is predicted for the most mass asymmetric projectile/target combination 54Cr + 248Cm. However, at SHIP this experiment was not possible so the reaction 64Ni + 238U was studied. If the proton shell closure is at Z=120 then an enhanced production rate and half-live of the element 120 would be expected. Depending on the magnitude of the stabilization due to the closed shell, one could expect up to a few events per week for the isotopes 299120 and 298120 produced in 64Ni + 238U reactions. The half-lives are expected to be of the order of some 10 μs, but in the end no luck, this time at least.

Depletion of the Ozone Layer in the 21st Century

A paper in Angewandte Chemie suggests that models predict that climate change will lead to an accelerated recovery of the ozone layer. However, reliable predictions are complicated by the ozone-depleting effect of N2O. If emissions of this greenhouse gas remain at current levels, by 2050 they could account for 30% of the ozone-destroying effects of chlorofluorocarbons at their peak.1

It is concluded that "the regulation of N2O levels in the atmosphere is not only important for the protection of Earth's climate (Kyoto Protocol) but also for the future evolution of the stratospheric ozone layer (Montreal Protocol). A reduction of N2O emissions would decrease the anthropogenic greenhouse effect and it would have a positive impact on the recovery of the ozone layer."

Depletion of the Ozone Layer in the 21st Century

Depletion of the Ozone Layer in the 21st Century, Dameris, Martin , Angewandte Chemie International Edition, Volume 9999, Number 9999, p.NA, (2009)

Element 112 (Uub) to become Copernicium, Cp

CoperniciumCoperniciumIn honour of scientist and astronomer Nicolaus Copernicus (1473-1543), the discovering team around Professor Sigurd Hofmann suggested the name copernicium with the element symbol Cp for the new element 112, discovered at the GSI Helmholtzzentrum für Schwerionenforschung (Center for Heavy Ion Research) in Darmstadt. It was Copernicus who discovered that the Earth orbits the Sun, thus paving the way for our modern view of the world. Thirteen years ago, element 112 was discovered by an international team of scientists at the GSI accelerator facility. A few weeks ago, the International Union of Pure and Applied Chemistry, IUPAC, officially confirmed their discovery. In around six months, IUPAC will officially endorse the new element's name. This period is set to allow the scientific community to discuss the suggested name copernicium before the IUPAC naming.

"After IUPAC officially recognized our discovery, we – that is all scientists involved in the discovery – agreed on proposing the name copernicium for the new element 112. We would like to honor an outstanding scientist, who changed our view of the world", says Sigurd Hofmann, head of the discovering team.

Copernicus was born 1473 in Torun; he died 1543 in Frombork, Poland. Working in the field of astronomy, he realized that the planets circle the Sun. His discovery refuted the then accepted belief that the Earth was the center of the universe. His finding was pivotal for the discovery of the gravitational force, which is responsible for the motion of the planets. It also led to the conclusion that the stars are incredibly far away and the universe inconceivably large, as the size and position of the stars does not change even though the Earth is moving. Furthermore, the new world view inspired by Copernicus had an impact on the human self-concept in theology and philosophy: humankind could no longer be seen as the center of the world.

With its planets revolving around the Sun on different orbits, the solar system is also a model for other physical systems. The structure of an atom is like a microcosm: its electrons orbit the atomic nucleus like the planets orbit the Sun. Exactly 112 electrons circle the atomic nucleus in an atom of the new element "copernicium".

Element 112 is the heaviest element in the periodic table, 277 times heavier than hydrogen. It is produced by a nuclear fusion, when bombarding zinc ions onto a lead target. As the element already decays after a split second, its existence can only be proved with the help of extremely fast and sensitive analysis methods. Twenty-one scientists from Germany, Finland, Russia and Slovakia have been involved in the experiments that led to the discovery of element 112.

Since 1981, GSI accelerator experiments have yielded the discovery of six chemical elements, which carry the atomic numbers 107 to 112. The discovering teams at GSI already named five of them: element 107 is called bohrium, element 108 hassium, element 109 meitnerium, element 110 darmstadtium, and element 111 is named roentgenium.

Gallium Trojan horse strategy defeats drug-resistant bacteria

An article in the Journal of Clinical Investigation outlines how a new antimicrobial approach kills bacteria in laboratory experiments and eliminate life-threatening infections in mice by interfering with a key bacterial nutrient. Iron is critical for the growth of bacteria and for their ability to form biofilms, slime-encased colonies of microbes that cause many chronic infections. "Gallium acts as a Trojan horse to iron-seeking bacteria," said Pradeep Singh (senior author). "Because gallium looks like iron, invading bacteria are tricked, in a way, into taking it up. Unfortunately for the bacteria, gallium can't function like iron once it's inside bacterial cells."

The work is by by workers from the University of Iowa and the University of Cincinnati. Rather than trying to find agents that best killed bacteria in test tubes, the researchers sought to intensify the stress imposed on microbes by one of the body's own defense mechanisms. The study's senior author Singh explained "The competition for iron is critical in the struggle between bacteria and host. The body has potent defense mechanisms to keep iron away from infecting organisms, and invaders must steal some if they are to survive."

"Because iron is so important in infection, we thought infecting bacteria might be vulnerable to interventions that target iron," explained Yukihiro Kaneko, senior fellow in microbiology at the UW and the study's lead author. To accomplish this, the researchers used gallium, a metal related in some ways to iron.

The researchers showed that gallium killed microbes, and prevented the formation of biofilms. Importantly, gallium's action was intensified in low iron condition, like those that exist in the human body. Gallium was even effective against strains of Pseudomonas aeruginosa from cystic fibrosis patients that were resistant to multiple antibiotics. In mice, gallium treatment blocked both chronic and acute infections caused by this bacterium. The idea of using gallium as a substitute for iron was developed by a group led by Bradley Britigan, a researcher at the University of Cincinnati and a co-author on this study.

Polonium: did it kill Alexander Litvinenko?

Polonium metal structurePolonium metal structureIt is suggested that poisoning by polonium-210 may have caused the death of Alexander Litvinenko, said to be a former Russian spy, in November 2006. Following his death at the end of November 2006, traces of polonium were found at several places he had visited before becoming ill. Before his death it was thought that thallium, or even radiothallium, might have been the cause of his illness. At the time of writing it is not clear who killed him, but not surprisingly the Russians deny it. Polonium-210 decays through the emission of α-particles and these emissions are noramlly easy to stop, but they are very dangerous if the polonium is inside the body.

Polonium is radioactive and present only in extremely low abundances in the environment. It is quite metallic in nature despite its location beneath oxygen in the periodic table. It is made in very small quantities through a nuclear reaction of bismuth. Neutron irradiation of 209bismuth (atomic number 83) gives 210polonium (atomic number 84).

209Bi + 1n → 210Po + e-

Polonium-210, 210Po, transmutes into the lead isotope 206Pb by the emission of an α-particle. The half life for this process is just over 138 days meaning that after 138 days one-half of the original 210Po has disappeared and after 2 times 138 days 3/4 has gone.

21084Po → 20682Pb + 42He

The short half life of polonium-210 and the heat generated with the above radioactive decay means that polonium metal generates considerable heat (141 W), meaning that the metal and its compounds self-heat. This is a useful property and polonium can be used as a small heat source (if expensive!). It can be used in space satellites for this purpose and is especially desirable as there are no moving parts. It was also used in the lunar rovers to keep internal parts warm during the frigid lunar nights.

Polonium metal is unique in that it is the only element whose structure (known as the α-form) is a simple cubic array of atoms in which each atom is surrounded by six other polonium atoms. On gentle warming to 36°C, this converts into a second form known as the β-form.

Polonium dioxidePolonium dioxidePolonium dissolves in acids to form pink hydrated Po(II), presumably as[Po(OH2)6]2+. This seems to oxidize to yellow Po(IV) species perhaps as a consequence of oxidizing agents produced through the α-particle induced decay of water. The polonium(II) oxide PoO is known but this oxidizes easily to the Po(IV) oxide PoO2.

Polonium dichloridePolonium dichlorideThe Po(II) halides PoX2 (X = Cl, Br, I) are known (the chloride and bromide are particularly well characterised) while all the Po(IV) halides PoX4 (X = F, Cl, Br, I) are known.

There are few crystallographically characterised polonium compounds largely because not many researchers work with polonium and the difficulties associated with characterising such radioactive compounds. The 14-electron polonium(IV) anion [PoI6]2– is strictly octahedral meaning the lone pair is sterochemically inactive.

Metal plated Venus?

Venus Cloud TopsVenus Cloud Tops
The BBC reported a few weeks ago that parts of Venus may be lead plated. David Whitehouse reports that

"The highlands of Venus are covered by a heavy metal 'frost', say planetary scientists from Washington University.

Because it is hot enough to melt lead at the surface, metals vaporise and condense at cooler, higher elevations.

This may explain why radar observations made by orbiting spacecraft show that the highlands are highly reflective.

Detailed calculations, to be published in the journal Icarus, suggest that lead and bismuth are to blame for giving Venus its bright, metallic skin."

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Copyright 1993-2011 Mark Winter [The University of Sheffield and WebElements Ltd, UK]. All rights reserved.