Rarely astatine

Our last chance to view very active elements occurs in Group 7A(17). The halogens begin with fl uorine (F), the strongest electron grabber of all. Chlorine (Cl), bromine (Br), and iodine (I) also form compounds with most elements, and even rare astatine (At) is thought to be reactive [Group 7A(17) Family Portrait, p. 448]. 

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.)... 

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. ... 

Tracer studies of the chemical properties showed that astatine was soluble in organic solvents, could be reduced to the —1 state, and had at least two positive oxidation states. These studies were made on solutions of 10-11 to KL15 molar astatine (29). The similarity between astatine and iodine was found to be less close than that between technetium and rhenium or that between promethium and the other rare earths (30). 

The halogens (Group Vllb) directly precede the rare gases in the Periodic Table. They are fiourine (Z — 9), chlorine (Z = 17), bromine (Z 35), iodine (Z = 53), and the recently discovered astatine (Z 86). 

Astatine is a member of the halogen family, elements in Group 17 (VlIA) of the periodic table. It is one of the rarest elements in the universe. Scientists believe that no more than 25 grams exist on Earth s surface. All isotopes of astatine are radioactive and decay into other elements. For this reason, the element s properties are difficult to study. What is known is that it has properties similar to those of the other halogens—fluorine, chlorine, bromine, and iodine. Because it is so rare, it has essentially... 

Astatine is far too rare to have any uses. Some research suggests a possible medical use, however. Astatine is similar to the elements above it in Group 17 (VIIA) of the periodic table, especially iodine. One property of iodine is that it tends to collect in the thyroid gland. The thyroid is a gland at the base of the neck that controls many body functions. 

The last element of the group of metalloids is astatine. It has been estimated that the whole Earth s crust contains less than 44 mg astatine and this element with the atomic number 85 can thus be considered one of the rarest naturally occurring elements on Earth. All isotopes of this radioactive element have short half-lives and are products of several radioactive decay series. At (ti/2 = 54 s) occurs in one rare side branch of the decay series while At, one of the products of a side branch of the Po decay series, undergoes a very fast P decay (ti/2 = IxlO s). 

Because all the HA and VIIA elements undergo similar reactions, the general equation, written above, represents 20 reactions. We omit radium and astatine, the rare and highly radioactive members of the families. 

Not much is known about astatine because it is very rare, is radioactive, and decays very quickly. Would you predict the chemical and physical properties of astatine to be more... 

Three of the four elements missing from the Periodic Table of 1925—technetium, promethium, and astatine—were produced synthetically by transmutation in a way similar to that by which the silver was transmuted into cadmium. The fourth missing element, francium, was first discovered by a rare observation of natural alpha-decay in the element actinium. 

In contrast to oxygen, shown here in its liquid form, the element astatine is so rare that there is only a small fraction of an ounce of it in the entire hard crust of the earth. 

In Group 7A(17), fluorine and chlorine have the condensed electron configuration [noble gas] ns np, as do the other halogens (Br, I, At). Little is known about rare, radioactive astatine (At), but all the others are reactive nonmetals that occur as diatomic molecules, X2 (where X represents the halogen). All form ionic compounds with metals (KX, MgX2), covalent compounds with hydrogen (HX) that yield acidic solutions in water, and covalent compounds with carbon (CX4). 

Metalloid is a term for elements that are sort-of metals, and sort-of not metals. Sometimes this group of elements is referred to as semimetals. To be more precise, these elements exhibit some of the physical and chemical properties of metals. Generally metalloids have some electrical conductivity, but not nearly as much as true metals. Because of these ambiguous definitions, even which elements are called metalloids can vary. Usually boron, silicon, germanium, arsenic, antimony, and tellurium are included as metalloids sometimes polonium and astatine rarely selenium. 

Some of the properties of the group 7A elements, the halogens, are given in TABLE 7.7. Astatine, vdiich is both extremely rare and radioactive, is omitted because many of its properties are not yet known. 

What may be said about these branches The producers of natural astatine (the polonium isotopes) are by themselves extremely rare. For them alpha decay is not just predominant but practically the only radioactivity mechanism. Beta decays for them seem something like a mishap as can be clearly seen from the following data. 

There is only one beta decay event per 5 000 alpha decays of polonium-218. Things are even sadder for polonium-216 (1 per 7 000) and polonium-215 (1 per 200 000). The situation speaks for itself. The amount of natural francium on Earth is larger. It is produced by the longest-lived actinium isotope Ac (a half-life of 21 years) and its content is, of course, much higher than that of the extremely rare polonium isotopes capable of producing astatine. 

Halogen ha-l9-j9n [Sw, fr. hal- + -gen] (1842) n. The elements of group 7a of the periodic table fluorine, chlorine, bromine, and iodine (F, Cl, Br, and 1). The fifth member, astatine, is rare, radioactive, and unstable, with a half-life less than 9 h, so it is never seen in commerce. 

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. 

Not much is known about astatine because it is very rare, is radioactive, and decays very quickly. Would you predict the chemical and physical properties of astatine to be more like those of a metal or nonmetal Defend your answer on the basis of astatine s location on the periodic table. Elemental chlorine is obtained by the electrolysis of molten NaCl (Downs cell). Elemental fluorine is obtained by the electrolysis of KHE2 in a cell made of Monel metal (a stainless steel alloy). Both of these processes are dangerous. Why ... 

The elements fluorine, chlorine, bromine, iodine and astatine constitute the halogen group of the periodic table. Astatine is a radioactive, very rare element, which is treated, not in this chapter, butin Chapter 52 Radioactive elements. The Elements are designated halogens (= salt formers) due to their tendency to form salts with metals. 

Most of the elements found in nature have several isotopes. Elements with atomic number 83 (bismuth) and lower have at least one stable isotope, although some are also radioactive and unstable. From element number 84 (polonium) and upwards, all the elements lack stable isotopes. The nine elements 84-92 are called naturally occurring radioactive elements. They are polonium, astatine, radon, francium, radium, actinium, thorium, protactinium and uranium. They are all treated in this chapter. There are also an additional two radioactive elements, number 43 technetium and 61 promethium. However, they have been described in Chapter 28 Technetium and Chapter 17 Rare earths, respectively. 

Most important mineral Some isotopes of astatine are present in uranium and thorium minerals as part of their radioactive decay series. Astatine belongs to the most rare elements of all. Its total amount in the earth s crust is estimated to be less than 30 grams. 

Astatine is the heaviest of the halogens. There are about 20 isotopes known, aU of which are radioactive. The element name, from Greek astatos, unstable , also indicates this fact. The longest-Hved isotope, At, has a half-life of 8.1 hours. Astatine behaves chemically very much like iodine. People in contact with this very rare element would probably accumulate it in their thyroid gland. 

At the top of group 17, fluorine is the most reactive and astatine at the bottom is the least reactive. Astatine is rare and radioactive, but predictions about its reactions and physical properties are possible. Astatine should not replace any of the other halc ens from their compounds. 

The Group 7A elements fluorine, chlorine, bromine, iodine, and astatine are known collectively as the halogens, meaning salt producers. The name was first applied to chlorine because of its ability to combine with metals to form salts. All but the extremely rare and poorly characterized astatine are now known to have this same ability. Although there is the usual variation in group properties, the striking similarities among these elements are reminiscent of those of the alkali and alkaline-earth metals. 

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