Astatine, elemental halogenation

Another previously unknown element, astatine (element 85, the heaviest of the halogens) was made at Berkeley in 1940 by bombarding bismuth with alpha particles. Again, Segre was among the team of chemists who showed it was a new element. 

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. 

Calcium reacts with the halogens— fluorine, chlorine, bromine, iodine, and astatine. The halogens are the elements that make up Group 17 (VIIA) of the periodic table. Calcium also reacts readily with cold water, most acids, and many non-metals, such as sulfur and phosphorus. For example, calcium reacts with sulfur ... 

Under ordinary conditions, the elemental halogens (except astatine) exist as covalent, diatomic molecules, acquiring the electronic configuration of the next noble gas by sharing one pair of electrons between two atoms. Their appearance ranges from a pale yellow gas (F2), through a dark red liquid (Br2), to an almost black, crystalline solid (I2). Bromine is unique in being the only nonmetallic element that exists as a liquid under ordinary conditions. Iodine crystals do not melt at atmospheric pressures, but sublime directly into the gas phase. 

Now let s slide to the left in the periodic table and consider the column of elements fluorine, chlorine, bromine, iodine, and astatine. Each of these elements has one less electron than does its neighboring inert gas. These elements are called the halogens. (The discussion that follows does not include astatine because this halogen is very rare.)... 

The halogens are a family of elements appearing on the right side of the periodic table, in the column just before the inert gases. The elements in this group—fluorine, chlorine, bromine, iodine, and astatine—show some remarkable similarities and some interesting trends in chemical behavior. The similarities are expected since the... 

The first column of the periodic table, Group 1, contains elements that are soft, shiny solids. These alkali metals include lithium, sodium, potassium, mbidium, and cesium. At the other end of the table, fluorine, chlorine, bromine, iodine, and astatine appear in the next-to-last column. These are the halogens, or Group 17 elements. These four elements exist as diatomic molecules, so their formulas have the form X2 A sample of chlorine appears in Figure EV. Each alkali metal combines with any of the halogens in a 1 1 ratio to form a white crystalline solid. The general formula of these compounds s, AX, where A represents the alkali metal and X represents the halogen A X = N a C 1, LiBr, CsBr, KI, etc.). 

C09-0133. Among the halogens, only one known molecule has the formula X 7. It has pentagonal bipyramidal geometry, with five Y atoms in a pentagon around the central atom X. The other two Y atoms are in axial positions. Draw a ball-and-stick model of this compound. Based on electron-electron repulsion and atomic size, determine the identities of atoms X and Y. Explain your reasoning. (Astatine is not involved. This element is radioactive and highly unstable.)... 

Halogens The elements—fluorine, chlorine, bromine, iodine, and astatine—that make up Group 17 of the periodic table. 

A stage org chem) An early stage in a thermosetting resin reaction characterized by linear structure, solubility, and fusibility of the material. a, staj astatine chem A radioactive chemical element, symbol At, atomic number 85, the heaviest of the halogen elements. as-t3,ten asterism (spect) A star-shaped pattern sometimes seen in x-ray spectrophotographs. as-t3,riz-om ... 

The halogens are the family of nonmetal elements in group 17 (VIIA) that are located just to the right of the oxygen group 16 on the periodic table of chemical elements. They are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). 

Astatine does not have stable or useful compounds. Like a halogen, it will form halogen salts with a few other elements. No significant astatine commercial compounds have been produced with the exception of astatine-211, which has a half-life of just over seven hours and is used as a radioactive tracer for thyroid diseases. 

Astatine, generally speaking, is a difficult isotope to study from a chemical viewpoint because no stable isotopes exist. Although the study of the chemical properties of astatine began over 40 years ago (44), the element s precise behavior is still in doubt. The chemical similarity between astatine and its nearest halogenic neighbor, iodine, is not always obvious. In many cases the astatine tracer has not... 

In 1940 D. R. Corson, K. R. Mackenzie, and E. Segre at the University of California bombarded bismuth with alpha particles (26, 27). Preliminary tracer studies indicated that they had obtained element 85, which appeared to possess metallic properties. The pressure of war work prevented a continuation of these studies at the time. After the war, the investigators resumed their work, and in 1947 proposed the name astatine, symbol At, for their element. The name comes from the Greek word for unstable, since this element is the only halogen without stable isotopes (28). The longest lived isotope is At210 with a half-life of 8.3 hours and a very high activity. 

The halogens will be restricted to chlorine, bromine and iodine since fluorine, as the most electronegative element, does not function as the central atom in a complex and astatine has only short-lived, radioactive isotopes, so that very little of its coordination chemistry has been investigated.2 ... 

This review will attempt to deal with the chemistry of the halogens appropriate to those compounds considered as coordination compounds. It will not include reference to astatine, which is covered by the general reviews listed above and for which little chemistry is known at all, and almost none as a coordinated ligand. Since the chemistry of the halides of individual elements is treated in the chapters for those elements, this section will be concerned with an overview of the general properties of the group. 

All the elements of the halogen family except astatine occur in nature in the form of their compounds. Because of their marked chemical activity, they are never found in nature in the uncombined state. 

In 1940, Corson, Mackenzie, and Segre announced the production of an isotope of element 85, astatine (At), which is the last member of the halogen family. This synthesis involved bombardment of bismuth with alpha particles in a cyclotron ... 

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