Astatine: reactivity

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 reactivity hazards of this well defined group of oxidants towards other materials decrease progressively from fluorine, which reacts violently with most materials (except for those metals on which resistant fluoride films form), through chlorine and bromine to iodine. Astatine may be expected to continue this trend. The individual entries are ... 

It has been suggested52 that in the pre-equilibrium step of astatination, the reagent 9 undergoes heterolytic fission (equation 12) forming the most reactive At+ ion, which is responsible for hydrogen replacement in the aromatic ring. 

Group VII, the halogen group The halogens (fluorine, chlorine, bromine, iodine, and astatine) are the most strongly non-metallic elements. They are very reactive chemically, and form many compounds. Their chemistry is discussed in Chapters 9 and 13. 

Barium is an active metal. It combines easily with oxygen, the halogens, and other non-metals. The halogens are Group 17 (VIIA) of the periodic table and include fluorine, chlorine, bromine, iodine, and astatine. Barium also reacts with water and with most acids. It is so reactive that it must be stored under kerosene or some similar petroleum-based liquid to prevent it from reacting with oxygen and moisture in the air. Of the alkaline earth family, only radium is more reactive. 

Chlorine is a member of the halogen family. Halogens are the elements that make up Group 17 (VIIA) of the periodic table, a chart that shows how elements are related to one another. They also include fluorine, bromine, iodine, and astatine. Chlorine is highly reactive, ranking only below fluorine in its chemical activity. 

The halogens—fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At)—are active nonmetals. Because of their chemical reactivity, they don t exist as free elements in nature. Their chemical behavior is characterized by a tendency to gain one electron to complete their valence-electron configuration and form a 1 — ion with a noble-gas configuration. Chlorine, for example, has the configuration [Ne]3s 3p. ... 

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). 

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]. 

Figure 6.7-6. Precursors used for residualizing radio-astatination of monoclonal antibodies and peptides. Chemically reactive groups on the precursors are shaded, and site for radio-astatination of the precursor is indicated in black and with an asterisk. SAB N-succinimidyl 3-astatobenzoate SAPC N-succinimidyl 5-astato-3-pyridinecarboxylate.

The other elements in column 2 are also water-reactive to varying degrees. These include calcium, strontium, barium, and radium, which is radioactive. The halogens in column 7 are nomnetals. They may be solids, liquids, or gases. Fluorine and chlorine are gases at normal temperatures and pressures. Bromine is a liquid to 58°C and produces vapor rapidly when above that temperature. Iodine is a solid. Astatine is also in column 7. It is radioactive however, such a small amount has ever been found that you are not likely to encounter it. 

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