How are new elements discovered?

Several experimental techniques have been used to make new chemical elements.

Some of these include

i)              heavy ion transfer reactions,

                 ii)      cold or hot fusion evaporation reactions,

iii)             neutron capture reactions,

                Iv)       light-ion charged particle induced reactions, and

                 V)        even nuclear explosions.

These techniques each have advantages and disadvantages making them suitable for studying nuclei in certain regions.

The types of nuclear reactions that have been successfully used to produce new elements in the last decade are cold fusion reactions and hot fusion reactions. 

Cold fusion reactions use beam and target nuclei that are closer to each other in mass in order to produce a compound nucleus (the complete fusion of one target nucleus with one beam nucleus) with generally lower excitation energy that typically requires evaporation of one or no neutrons. This generates fewer neutron-rich isotopes of an element that have higher survival probabilities with respect to fission, but have lower fusion probabilities. An example of this type of reaction is⁷⁰Zn + ²⁰⁸Pb → ²⁷⁷112 + 1n with a cross-section of ~1 picobarn.

Because the 112 isotope ultimately decays by α emission to known nuclei [namely isotopes of elements 102 (No) and 104 (Rf)], identification of this element is straightforward. Hot fusion reactions use more asymmetric beam and target nuclei, produce a compound nucleus with generally higher excitation energy that typically requires evaporation of three to five neutrons, generate more neutron-rich isotopes of an element, have lower survival probabilities with respect to fission, but have higher fusion probabilities.

 An example of this type of reaction is ⁴⁸Ca + ²⁴⁴Pu → ²⁸⁸114 + 4n with a cross-section of ~1 pb. Because of the neutron-richness of this isotope of element 114, it never subsequently decays to any known isotope, and thus its identification is more problematic. Cold fusion reactions have been successful in producing elements 104—112 and hot fusion reactions have recently provided evidence for elements 113—118.

New names for elements 114 and 116

New Names for Elements 114 and 116

Scientists of the Lawrence Livermore National Laboratory (LLNL)-Dubna collaboration proposed the names as Flerovium for element 114, with the symbol Fl, and Livermorium for element 116, with the symbol Lv, late last year.The International Union of Pure and Applied Chemistry (IUPAC) officially approved new names for elements 114 and 116, the latest heavy elements to be added to the periodic table, on May 31, 2012. See IUPAC news ite

Flerovium (atomic symbol Fl) was chosen to honor Flerov Laboratory of Nuclear Reactions, where superheavy elements, including element 114, were synthesized. Georgiy N. Flerov (1913-1990) was a renowned physicist who discovered the spontaneous fission of uranium and was a pioneer in heavy-ion physics. He is the founder of the Joint Institute for Nuclear Research. In 1991, the laboratory was named after Flerov -- Flerov Laboratory of Nuclear Reactions (FLNR).

Livermorium (atomic symbol Lv) was chosen to honor Lawrence Livermore National Laboratory (LLNL) and the city of Livermore, Calif. A group of researchers from the Laboratory, along with scientists at the Flerov Laboratory of Nuclear Reactions, participated in the work carried out in Dubna on the synthesis of superheavy elements, including element 116. (Lawrencium -- Element 103 -- was already named for LLNL's founder E.O. Lawrence.)

The IUPAC states Livermorium was chosen because over the years scientists at Livermore have been involved in many areas of nuclear science: the investigation of fission properties of the heaviest elements, including the discovery of bimodal fission, and the study of prompt gamma-rays emitted from fission fragments following fission; the investigation of isomers and isomeric levels in many nuclei; and the investigation of the chemical properties of the heaviest elements.

"These names honor not only the individual contributions of scientists from these laboratories to the fields of nuclear science, heavy element research, and superheavy element research, but also the phenomenal cooperation and collaboration that has occurred between scientists in these two countries," said Bill Goldstein, associate director of LLNL's Physical and Life Sciences Directorate.

Scientists at LLNL have been involved in heavy element research since the Laboratory's inception in 1952 and have been collaborators in the discovery of six elements -- 113,114,115,116,117 and 118.

Livermore also has been at the forefront of investigations into other areas related to nuclear science such as cross-section measurements, nuclear theory, radiochemical diagnostics, separations chemistry including rapid automated aqueous separations, actinide chemistry, heavy-element target fabrication and nuclear forensics.

HOW THEY ARE CREATED

The creation of elements 116 and 114 involved smashing calcium ions (with 20 protons each) into a curium target (96 protons) to create element 116. Element 116 decayed almost immediately into element 114. The scientists also created element 114 separately by replacing curium with a plutonium target (94 protons).

The creation of elements 114 and 116 generate hope that the team is on its way to the "island of stability," an area of the periodic table in which new heavy elements would be stable or last long enough for applications to be found.

The official names will be published in the July issue of the IUPAC journal, Pure and Applied Chemistry.

The process of discovery and naming of an element is a long one. Experiments first glimpsed element 114 in 1998 and element 116 in 2001, with continuing experiments satisfying the discovery criteria in 2004 and 2006, and confirmatory experiments by other laboratories in 2007 – 2010.

The collaboration is led by Dr. Yuri Ts. Oganessian. The participants in these experiments include:

Dubna: Yu.Ts. Oganessian, V.K. Utyonkov, F.Sh. Abdullin, A.N. Polyakov, I.V. Shirokovsky, Yu.S. Tsyganov, R.N. Sagaidak, G.G. Gulbekian, S.L Bogomolov, B.N. Gikal, A.N. Mezentsev, V.G. Subbotin, A.M. Sukhov, A.A. Voinov, K. Subotic, G.K. Vostokin, M.G. Itkis, V.I. Zagrebaev, R.I. Il’kaev, S.P. Vesnovskii

LLNL: K.J. Moody, D.A. Shaughnessy, M.A. Stoyer, J.M. Kenneally, C.A. Gregorich, J.H. Landrum, R.W. Lougheed, J.B. Patin, N.J. Stoyer, J.F. Wild, and P.A. Wilk

How to Favor an E2 Mechanism

       How to Favor an E2 Mechanism

       How to Favor an E2 Mechanism

1. Use a secondary or tertiary alkyl halide if possible.

Why: Because steric hindrance in the substrate will inhibit substitution.

2. When a synthesis must begin with a primary alkyl halide, use a bulky base.

Why: Because the steric bulk of the base will inhibit substitution.

3. Use a high concentration of a strong and nonpolarizable base such as an alkoxide.

Why: Because a weak and polarizable base would not drive the reaction toward a bimolecular reaction, thereby allowing unimolecular processes (such as SN1 or E1 reactions) to compete.

4. Sodium ethoxide in ethanol(EtONa/EtOH)and potassium tert-butoxide intertbutyl alcohol(t-BuOK/t-BuOH)are bases typically used to promote E2 reactions.

Why: Because they meet criterion 3 above. Note that in each case the alkoxide base is dissolved in its corresponding alcohol. (Potassium hydroxide dissolved in ethanol or tert-butyl alcohol is also sometimes used, in which case the active base includes both the alkoxide and hydroxide species present at equilibrium.)

5. Use elevated temperature because heat generally favors elimination over  substitution.

Why: Because elimination reactions are entropically favored over substitution reactions (because the products are greater in number than the reactants). Hence ∆S° in the Gibbs free-energy equation, ∆ G°=∆ H°   -  T  ∆S° is significant, and ∆S° will be increased by higher temperature since T is a coefficient, leading to a more negative (favorable) ∆G°.