Astatine abundance

Radon, the heaviest of the noble gases, has been much publicized in recent years because of a fear that low-level exposures increase the risk of cancer. Like astatine and francium, its neighbors in the periodic table, radon is a radioactive element with only a minute natural abundance. It is produced by radioactive decay of the radium present in small amounts in many granitic rocks, and it can slowly seep into basements, where it remains unless vented. If breathed into the lungs, it can cause radiation damage. 

F and Cl are moderately abundant elements, principal sources being fluorite CaF2 and halite NaCl, from which the very electronegative elements are obtained by electrolysis. Bromine is mainly obtained by oxidation of Br- found in salt water iodine occurs as iodates such as Ca(I03)2. Astatine is radioactive and only minute amounts are found in nature. Chlorine is used... 

Several chlorine isotopes exist with mass numbers ranging between 32 and 40. The two stable isotopes are Cl and Cl with natural abundances of 75.77% and 24.23% respectively, while the others are radioactive. Bromine also has two stable isotopes, Br and Br, with natural abundances of 50.69% and 49.31% respectively, while the others are radioactive. Iodine has only one stable isotope, and numerous radioactive ones are known. Astatine is known only as its radioisotope see Radioactive Decay). 

Fig. 16.1 Relative abundances of the halogens (excluding astatine) in the Earth s crust and seawater. The data are plotted on a logarithmic scale. The units of abundance are parts per billion (1 billion = 10 ).

The total amount of astatine in the Earth s crust is less than 30 g, which makes it the least abundant element on Earth. 

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