Astatine, elemental reactions with

The most important transmutations by a particles are of the (a,p) and (a,n) types. The (a,p) processes (for example, Na23(a,p)Mg26) are common with targets of low atomic weights (Z > 25) as has been seen, these were the first artificial transmutations to be studied. The (a,n) reactions (and the closely related reactions in which two, three, or more neutrons are ejected by a particles of high energy) are of considerable interest in connection with the synthesis of the transuranium elements and of astatine (element 85). The following are typical and important examples ... 

Elements 43 (technetium), 61 (promethium), 85 (astatine), and all elements with Z > 92 do not exist naturally on the Earth, because no isotopes of these elements are stable. After the discovery of nuclear reactions early in the twentieth century, scientists set out to make these missing elements. Between 1937 and 1945, the gaps were filled and three actinides, neptunium (Z = 93), plutonium (Z = 94), and americium (Z = 95) also were made. 

Astatine - the atomic number is 85 and the chemical symbol is At. The name derives from the Greek astatos for unstable since it is an unstable element. It was first thought to have been discovered in nature in 1931 and was named alabamine. When it was determined that there are no stable nuclides of this element in nature, that claim was discarded. It was later shown that astatine had been synthesized by the physicists Dale R. Corson, K. R. Mackenzie and Emilio Segre at the University of California lab in Berkeley, California in 1940 who bombarded bismuth with alpha particles, in the reaction Bi ( He, 2n ) "At. Independently, a claim about finding some x-ray lines of astatine was the basis for claiming discovery of an element helvetium, which was made in Bern, Switzerland. However, the very short half-life precluded any chemical separation and identification. The longest half-life associated with this unstable element is 8.1 hour °At. 

The compound BrF can be prepared by fluorinating bromine not with elemental fluorine but with a higher bromine fluoride in a disproportionation reaction (equations 33 and 34). Fluorination of halides (equation 35) instead of elemental halogen is sometimes preferable, leading to purer products. Interhalogen compounds also include astatine ones such as AtCl, AtBr, and Atl. 

Phosphorus combines easily with the halogens. The halogens are the elements that make up Group 17 (VIIA) of the periodic table. They include fluorine, chlorine, bromine, iodine, and astatine. For example, the reaction between phosphorus and chlorine is ... 

The metalloid elements include boron, silicon, germanium, arsenic, antimony, tellurium, and astatine. Ligand exchange reactions complete much faster for silicon complexes when compared with carbon complexes because the silicon atom can form a hypervalent transition state that carbon cannot. 

Fluorine reacts with water to produce oxygen, O2, and ozone, O3. This is strange in comparison with alkali metals. Next, chlorine reacts with water to produce hypochlorite, OCl . Bromine and iodine behave similarly, producing hypobromite OBr and hypoiodite 01 . Nothing is known about the reaction of astatine with water. Apart from the exceptional behavior of fluorine,there is no doubt that we have a family of elements. This family is different from the noble gases and from the alkali metals. 

Elements 85 and 87 fall into the region covered by the natural decay series and could therefore be expected to be fed by rare decay branches. As early as 1914, a particles were observed in carefully purified Ac (Z = 89), which implied the formation of element 87 (Meyer et al. 1914). However, the work of Marguerite Perey in 1939 is credited with the discovery of element 87 - the last discovery of a new element in nature (Perey 1939a, b). She proved that a 21 min P emitter ( 87) growing from Ac had chemical properties akin to cesium, and named the element francium (Fr). Element 85, astatine (At), the heaviest known halogen, was first produced artificially in 1940 as 85 (Ty2 = 7 h) by (a,2n) reaction on ° Bi (Corson et al. 1940a, b) before short-lived isotopes were found also in rare branches of the decay series. 

There are at the moment 115 known elements with atomic numbers 1-115. Of these, 93-115 exist only as the results of nudear reactions. Strictly speaking the natural elements are less numerous than 92 as some occur only as radioactive isotopes with such short half-hves that their concentrations in nature are extremely low. These special elements are 43 technetium, 61 promethium, 84 polonium, 85 astatine, 86 radon, 87francium, 88 radium and 89 actinium. 

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