Astatine

Astatine is the heaviest member of group 17 and is known only in the form of radioactive isotopes, all of which have short half-hves. The longest lived isotope is At (t = 8.1h). Several isotopes are present naturally as transient products of the decay of uranium and thorium 

The At isotope may be separated by vacuum distillation. In general. At is chemically similar to iodine. Tracer studies (which are the only sources of information about the element) show that At2 is less volatile than I2, is soluble in organic solvents, and is reduced by SO2 to At which can be coprecipitated with Agl or TIL Hypochlorite, [C10], or peroxydisulfate, [S20g], oxidizes astatine to an anion that is carried by (e.g. coprecipitation 

The Halogens Fluorine, Chlorine, Bromine, Iodine and Astatine 

The lustrous, purple-black metallic sheen of resublimed crystalline iodine was first observed 

If the necessary iodine input is insufficient the thyroid gland enlarges in an attempt to gamer more iodine addition of 0.01% Nal to table salt (iodized salt) prevents this condition. Tincture of iodine is a useful antiseptic. 

The first iodine-containing mineral (Agl) was discovered in Mexico in 1825 but the discovery of iodate as an impurity in Chilean saltpetre in 1840 proved to be more significant industrially. The Chilean nitrate deposits provided the largest proportion of the world s iodine until overtaken in the late 1960s by Japanese production from natural brines (pp. 796, 799). 

In addition to its uses in photography and medicine, iodine and its compounds have been much exploited in volumetric analysis (iodometry and iodimetry, p. 864). Organoiodine compounds have also played a notable part in the development of synthetic organic chemistry, being the first compounds used in A. W. von Hofmann s alkylation of amines (1850), A. W. Williamson s synthesis of ethers (1851), A. Wurtz s coupling reactions (1855) and V. Grignard s reagents (1900). 

ATOMIC MASS 210 (most stable isotope) VALENCE 1, 3, 5, and 7 OXIDATION STATE  

ORIGIN OF NAME From the Greek word astatos, which means unstable. All of its isotopes are unstable. 

ISOTOPES All 41 isotopes of astatine are radioactive, with half-lives ranging from 125 nanoseconds to 8.1 hours. The isotope As-210, the most stable isotope with an 8.1-hour half-life, is used to determine the atomic weight of astatine. As-210 decays by alpha decay into bismuth-206 or by electron capture into polonium-210. 

Astatine is located just below iodine, which suggests that it should have some of the same chemical properties as iodine, even though it also acts more hke a metal or semimetal than does iodine. It is a fairly heavy element with an odd atomic number, which assisted chemists in learning more about this extremely rare element. The 41 isotopes are man-made in atomic reactors, and most exist for fractions of a second. The elements melting point is about 302°C, its boiling point is approximately 337°C, and its density is about 7g/cm.  

Astatine is the heaviest and densest of the elements in group 17 (VIIA). It is difficult to determine the chemical and physical properties and characteristics of astatine because it is present in such small quantities that exist for extremely short periods of time. Many of its characteristics are inferred through experiments rather than by direct observations. 

Meisenberg, Gerhard, and Simmons, William H. (1998). Principles of Medical Biochemistry. St Louis, MO Mosby. 

DNA deoxyribonucleic acid—the natural polymer that stores genetic information in the nucleus of a cell 

Astatine is a radioactive halogen (the heaviest of the halogen elements) and is a solid at room temperature. Dale R. Carson, K. R. MacKenzie, and Emilio Segre of the University of California produced the element in 1940 by bombarding an isotope of bismuth ( ° Bi) with alpha particles. The origin of the name astatine is the Greek word astatos, which means unstable.  

Astatine is found in only vanishingly small amounts in nature—it is believed that only 30 grams (1 ounce) of the element are present in Earth s crust at any one time. It is produced naturally when the elements uranium and thorium decay. Astatine can also be produced in a nuclear reactor by the method used by its discoverers, according to the following reaction  

The most stable isotope of astatine is °At, which has a half-life of 8.1 hours. Other isotopes have mass numbers ranging from 193 to 223 and half-lives ranging from 125 nanoseconds ( At) to 7.2 hours ( At). Astatine is known to form interhalogen compounds with bromine (AtBr), chlorine (AtCl), and iodine (Atl). Additional compounds (HAt and CHjAt) have also been detected. 

The preparation of At is described in the text in terms of the abbreviated nuclear reaction g3Bi(a,2n) g5At. Expand this notation into a full equation for the reaction. 

Explain what happens when g Po loses a p-particle. 

Dichlorine is one of the most important industrial chemicals in the world. In 2004, the US produced 12.2 Mt of CI2 by 

The incorporation of flame retardants into plastics, textUes, electronic equipment (e.g. printed circuit boards) and other materials is big business, and demand in the US is expected to reach the equivalent of US 1.3 billion by 2008. The chart on the right shows the split between the three main categories of flame retardants in the US in 2003. A range of brominated organics is used commercially, the most important being  

Phosphorus-based flame retardants include tris(l,3-dichloroisopropyl) phosphate, used in pol5nirethane foams and polyester resins. Once again, there is debate concerning toxic side-effects of such products although these flame retardants may save lives, they produce noxious fumes during a fire. 

There are no stable isotopes of the heaviest halogen. It was originally prepared in 1940 by D. R. Corson, K. R. MacKenzie, and E. Segre by alpha bombardment of 

Its name is derived from the Greek as fa fos, meaning unstable. Although there are 20 known isotopes of astatine, At, with a half-life of 7.21 hours, remains one of the stablest. Given the instability of this element, it comes as no surprise that there is probably less than an ounce of astatine in the Earths crust, making it the rarest naturally occurring terrestrial element. Little is known about its chemistry. Most of what is known has been derived from work done with extremely dilute (about 10 M) aqueous solutions. 

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Taking francium as an example, it was assumed that the minute traces of francium ion Fr could be separated from other ions in solution by co-precipitation with insoluble caesium chlorate (VII) (perchlorate) because francium lies next to caesium in Group lA. This assumption proved to be correct and francium was separated by this method. Similarly, separation of astatine as the astatide ion At was achieved by co-precipitation on silver iodide because silver astatide AgAt was also expected to be insoluble. 

By considering the trends in the vertical groups of the Periodic Table, deduce possible answers to the following questions concerning the element astatine (At), atomic number 85. 

Astatine can be produced by bombarding bismuth with energetic alpha particles to obtain the relatively long-lived 209-211At, which can be distilled from the target by heating in air. 

The "time of flight" mass spectrometer has been used to confirm that this highly radioactive halogen behaves chemically very much like other halogens, particularly iodine. Astatine is said to be more metallic than iodine, and, like iodine, it probably accumulates in the thyroid gland. Workers at the Brookhaven National Laboratory have recently used reactive scattering in crossed molecular beams to identify and measure elementary reactions involving astatine. 

The fugitive radioactive element astatine can hardly be said to exist in nature though the punctillious would rightly point to its temporary participation in the natural radioactive series. Thus At (t i 54 s) occurs as a... 

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