Astatine atomic properties

On the basis of what you have learned about the physical and chemical properties and reactions of CI2/ Br2, and I2 and/or of HF, HCl, HBr, and HI, write an essay describing clearly what physical and chemical properties and reactions you would expect for elemental astatine (atomic number 85) and/or its acid, HAt (as designated by your instructor). 

The melting points show a pattern, or trend, down the group. It is therefore possible to predict that the melting point of astatine is approximately 380 °C. The same can be done with other physical properties, such as the melting points, and atomic properties, such as first ionization energy. 

The element exists as an intermediate in uranium and thorium minerals through their decay. There is no stable isotope. The longest-living isotope has a half-life of 8.3 hours. In the crust of the Earth, the total steady-state mass is estimated at a few tens of grams. Thus astatine is the rarest element (record ). A few atoms of this relative of iodine can be found in all uranium ore. It exhibits certain metallic properties. 

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. ... 

So far as the physical and chemical properties of astatine itself are concerned, not many new data have been published in the last 10-12 years however, a more thorough investigation of the literature has presented quite a few values of physicochemical—mainly thermodynamic—properties of At ions, of the At atom and of the hypothetical At2 molecule so far not commonly known (see Table 1). 

TABLE 1. Some physicochemical properties of astatine ions, atom and molecule (calculated values)... 

Norseyev and Nefedov75 used an experimental parameter—the so-called effective atomic number, Z —derived from the gas chromatographic behaviour of halogen compounds to make a rough assessment of some of the basic properties for a number of aliphatic astatine compounds. Table 9 provides the values of boiling temperatures for these compounds. 

One further element in this group, astatine, has been discovered but only a handful of atoms of it have ever been isolated. Its macroscopic properties, such as the color of the element, therefore remain unknown. 

Figure 3.14 Chlorine, bromine, and iodine (left to right) all belong to group VIIA(17) of the periodic table. Their atoms all have the same number of electrons in the valence shell and therefore similar chemical properties. However, they do not have similar appearances. At room temperature and under normal atmospheric pressure, chlorine is a pale yellow gas, bromine is a dark red liquid that readily changes into a gas, and iodine is a gray-black solid that changes into a purple gas when heated slightly. Astatine is the next member of the group after iodine. Try to think like Mendeleev and predict its color and whether it will be a liquid, solid, or gas under normal conditions. Electronic Structure and the Periodic Law 91...

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