oganesson (Og), a transuranium element that occupies position 118 in the periodic table and is one of the noble gases. Oganesson is a synthetic element, and in 1999 scientists at Lawrence Berkeley National Laboratory in Berkeley, California, announced the production of atoms of oganesson as a result of the bombardment of lead-208 with atoms of krypton-86. However, in 2002 this result was retracted after it was discovered that some of the data had been falsified. In 2006 scientists at the Joint Institute for Nuclear Research at Dubna, Russia, announced that oganesson had been made in 2002 and 2005 in a cyclotron by the nuclear reaction of calcium-48 at an energy of 245 million electron volts (MeV) with a californium-249 target, with three neutrons and one atom of oganesson as the reaction products. Nearly a millisecond after creation, the oganesson nucleus decays into another transuranium element, livermorium, by emitting an alpha particle (helium nucleus). No physical or chemical properties of oganesson can be directly determined, since only a few atoms of oganesson have been produced, but it is likely that oganesson is a gas at room temperature. The chemistry of oganesson, like radon, is expected to reflect its anticipated metalloid properties. In January 2016 the discovery of element 118 was recognized by the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP). The discoverers named it oganesson after Russian physicist Yuri Oganessian, who led the group at Dubna that discovered it and several other of the heaviest transuranium elements. The name oganesson was approved by IUPAC in November 2016.

Element Properties
atomic number118
atomic weight294
electron configuration(Rn)5f146d107s27p6
The Editors of Encyclopaedia Britannica This article was most recently revised and updated by Rick Livingston.
In full:
periodic table of the elements
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periodic table, in chemistry, the organized array of all the chemical elements in order of increasing atomic number—i.e., the total number of protons in the atomic nucleus. When the chemical elements are thus arranged, there is a recurring pattern called the “periodic law” in their properties, in which elements in the same column (group) have similar properties. The initial discovery, which was made by Dmitry I. Mendeleev in the mid-19th century, has been of inestimable value in the development of chemistry.

It was not actually recognized until the second decade of the 20th century that the order of elements in the periodic system is that of their atomic numbers, the integers of which are equal to the positive electrical charges of the atomic nuclei expressed in electronic units. In subsequent years great progress was made in explaining the periodic law in terms of the electronic structure of atoms and molecules. This clarification has increased the value of the law, which is used as much today as it was at the beginning of the 20th century, when it expressed the only known relationship among the elements.

History of the periodic law

The early years of the 19th century witnessed a rapid development in analytical chemistry—the art of distinguishing different chemical substances—and the consequent building up of a vast body of knowledge of the chemical and physical properties of both elements and compounds. This rapid expansion of chemical knowledge soon necessitated classification, for on the classification of chemical knowledge are based not only the systematized literature of chemistry but also the laboratory arts by which chemistry is passed on as a living science from one generation of chemists to another. Relationships were discerned more readily among the compounds than among the elements; it thus occurred that the classification of elements lagged many years behind that of compounds. In fact, no general agreement had been reached among chemists as to the classification of elements for nearly half a century after the systems of classification of compounds had become established in general use.

J.W. Döbereiner in 1817 showed that the combining weight, meaning atomic weight, of strontium lies midway between those of calcium and barium, and some years later he showed that other such “triads” exist (chlorine, bromine, and iodine [halogens] and lithium, sodium, and potassium [alkali metals]). J.-B.-A. Dumas, L. Gmelin, E. Lenssen, Max von Pettenkofer, and J.P. Cooke expanded Döbereiner’s suggestions between 1827 and 1858 by showing that similar relationships extended further than the triads of elements, fluorine being added to the halogens and magnesium to the alkaline-earth metals, while oxygen, sulfur, selenium, and tellurium were classed as one family and nitrogen, phosphorus, arsenic, antimony, and bismuth as another family of elements.

Attempts were later made to show that the atomic weights of the elements could be expressed by an arithmetic function, and in 1862 A.-E.-B. de Chancourtois proposed a classification of the elements based on the new values of atomic weights given by Stanislao Cannizzaro’s system of 1858. De Chancourtois plotted the atomic weights on the surface of a cylinder with a circumference of 16 units, corresponding to the approximate atomic weight of oxygen. The resulting helical curve brought closely related elements onto corresponding points above or below one another on the cylinder, and he suggested in consequence that “the properties of the elements are the properties of numbers,” a remarkable prediction in the light of modern knowledge.

Periodic Table of the elements concept image (chemistry)
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Classification of the elements

In 1864, J.A.R. Newlands proposed classifying the elements in the order of increasing atomic weights, the elements being assigned ordinal numbers from unity upward and divided into seven groups having properties closely related to the first seven of the elements then known: hydrogen, lithium, beryllium, boron, carbon, nitrogen, and oxygen. This relationship was termed the law of octaves, by analogy with the seven intervals of the musical scale.

Then in 1869, as a result of an extensive correlation of the properties and the atomic weights of the elements, with special attention to valency (that is, the number of single bonds the element can form), Mendeleev proposed the periodic law, by which “the elements arranged according to the magnitude of atomic weights show a periodic change of properties.” Lothar Meyer had independently reached a similar conclusion, published after the appearance of Mendeleev’s paper.

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