Thallium elemental properties

C21-0042. From Its position in the periodic table, predict the properties of thallium (Element 81). 

The vast range in elemental properties, from those of metallic elanents such as thallium and lead that have very low electronegativities of 1.8 and 1.9 (respectively) to those of the nonmetalUc elements such as oxygen and fluorine that have the highest electronegativities of 3.5 and 4.0 (respectively), results in the great chemical diversity of the elements in the p block. These elements include metals, alloys, simple covalent compounds, enormous covalent network compounds, simple binary ionic compounds, and complex chain and layered ionic compounds. 

Elemental composition T1 96.23%, 0 3.77%. ThaUium may be measured by various instrumental methods on an aqueous or acid solution of the metal oxide. Also, the compound can be identified by its physical and x-ray properties. Thallic oxide reverts to thallium oxide on heating above 100°C. 

Crookesite. In 1866 Baron Nils Adolf Erik Nordenskiold found among the collections at the Royal Museum in Sweden a rare mineral from Skrikerum, which C. G. Mosander had regarded as a copper selenide. When Baron Nordenskiold analyzed it, he found it to be a selenide of copper, silver, and thallium. Because it was the first mineral of which the recently discovered element thallium was shown to be an essential constituent, he named it crookesite in honor of Sir William Crookes, the discoverer of thallium (31). Although crookesite is very rare, selenium and thallium are often found associated in nature, and both of these elements, so different in chemical properties, were originally discovered in the same source, namely the slime in the lead chambers of sulfuric acid plants using seleniferous and thalliferous pyrite. 

Uranium-238 emits an alpha particle to become an isotope of thorium. This unstable element emits a beta particle to become the element now known as Protactinium (Pa), which then emits another beta particle to become an isotope of uranium. This chain proceeds through another isotope of thorium, through radium, radon, polonium, bismuth, thallium and lead. The final product is lead-206. The series that starts with thorium-232 ends with lead-208. Soddy was able to isolate the different lead isotopes in high enough purity to demonstrate using chemical techniques that the atomic weights of two samples of lead with identical chemical and spectroscopic properties had different atomic weights. The final picture of these elements reveals that there are several isotopes for each of them. 

One of the classical properties of the main group elements is that the stability of the lower oxidation states increases with atomic number, and the chemistry of thallium is a good example of this effect. In aqueous solution, the Tl+ ion is stable with respect to oxidation by the solvent and there is accordingly an extensive chemistry of this oxidation state. The similarities between Tl+ and the corresponding alkali metal cations have resulted in much interest in the use of this ion as a probe in biochemical systems, and the ease with which 205T1 NMR spectra can be recorded has also had an impact on such studies.277,278... 

The periodic trends in main-group elements become apparent when we compare the binary compounds they form with one specific element. All the main-group elements, with the exception of the noble gases and, possibly, indium and thallium, form binary compounds with hydrogen, so these hydrides can be examined to look for periodic trends. We meet the binary hydrides several times in this chapter and the next, so, at this stage, we confine the discussion to a brief survey and see how their properties reveal periodic behavior. 

Of course, what the students are really interested in is why thallium is poisonous. Surprisingly, thallium is toxic because it mimics potassium in the body. But why would thallium behave like potassium As we study the periodic table and chemical periodicity, there is no immediate reason to suspect that these two elements would have similar properties. A close look at the electron shell arrangement of thallium and potassium, however, reveals that both form +1 ions. Since Tl+ ions also happen to be similar in size to K+ ions, they are able to replace potassium ions in cellular processes. (Thallium poisoning is treated with a compound called Prussian blue, which binds to +1 ions and thus facilitates their removal from the body.) It is clear then that we cannot understand the toxicity of thallium without studying its atomic structure and electron distribution. But chemistry is only part of the story. The effects of thallium poisoning only make sense if the... 

Boron, aluminum, gallium, indium, and thallium are members of group 13 of the Periodic Table. Some important properties of these elements are given in Table 13.1.1. 

The atoms of the chemical elements, are, as I have already said, extremely complex, but their structure is not yet completely understood. To some part of each kind of atom its chemical properties and its spectrum are probably due. It is conceivable that this part may be the earliest to form, with its surrounding rings or envelopes at first not quite adjusted to permanent stability. With the final adjustment the isotopes as such should disappear, and the normal element be completed. This is speculation, and its legitimacy remains to be established. A careful comparison of the spectra of the elements from thallium up to uranium might furnish some evidence as to its validity. The spectrum of uranium, for example, may contain lines which really belong to some of its derivatives. 

Extrapolations within the respective groups of the Periodic Table should thus be an appropriate approach to predict the chemical behavior of superheavy elements [14]. Examples are the detailed treatments [16] of chemical and physical properties of the 7p elements 113 and 114, eka-thallium and eka-lead. Predictions of properties common to several superheavy elements were carried out for the design of group separations as a first step in chemical search experiments. Examples are the high volatility of elements 112 to 116 in the metallic state [17], or the formation of strong bromide complexes of elements 108 to 116 in solution [18]. 

Thallium, atomic no. 81 This element is better known for its poisonous properties and links with almost undetected deaths and Agatha Christie -type murder mysteries.2 Thallium compounds are used in some countries as cheap insecticides, particularly for killing cockroaches. Intake of this element causes stomach pains, vomiting and nausea, painful soles and palms of hands, limb weakness, double vision, involuntary eye movements, hallucina tions, characteristic hair loss and white lines across the nails. The symptoms are often mis-diagnosed as other diseases. Treatment is with the chemical Prussian Blue... 

In contrast to the other elements of group 13, thallium is considered a soft acid in Pearson s soft/hard acid classification (see Hard Soft Acids and Bases).This makes the element and its derivatives unique, and leads to its potentially most outstanding feature the properties of thallium are a subtle blend of some of the most desirable properties of numerous other metals (e.g. heavy alkali metals, silver, mercury, and lead). Thallium compounds are stable in both oxidation states (-1-1 and -1-3). The trivalent cation is quite a strong oxidation reagent, since it is reduced to T1+ easily (standard redox potential E°(TP+ — Tl" ") = -1.25 V). The ease of this reduction is utilized in certain organic reactions. 

Equation 4. Among the heavier elements in the B subgroup of the periodic table, thallium, lead, and bismuth are notable because their compounds resemble those of the elements with atomic numbers two lower thus the properties of Pb(II) compounds are similar to those of Hg(II) compounds, etc. (12). For this reason, we have chosen Pb(II) compounds as the principle bases for estimation of entropies of Hg(II) compounds with Equation 4. 

The Group 13 elements have the same relationship to the alkaline earth elements that the alkaline earth elements have to the alkali metals, that is, the group properties are modified by the presence of a third valence electron. The elements of Group 13 are boron, aluminum, gallium, indium, and thallium. Except for boron, which may be classified as a semimetal, these elements tend to show metallic properties. 

Practically all HTSC materials contain chemically active elements with the consequence that various degradation processes are bound to proceed accompanied by the loss of superconducting properties in air, and especially in moist atmospheres and electrolyte solution. Hence, it is essential to carry out electrochemical studies only in media for which degradation does not proceed or is very slow. These are, primarily, aprotic solvents, and also aqueous alkaline solutions of sufficiently high concentration, including those to which have been added salts of the elements of the HTSC components. Thus, in ordinary aqueous solutions, at not too low a pH one can study relatively stable thallium- and bismuth-based HTSCs, and also LCO and certain of its derivatives. 

Thallium is too expensive to have many practical applications. There are a few exceptions, however, that make use of special properties of the elements and its compounds. For example, thallium sulfide (TI2S) is sometimes used in photocells. Photocells are devices that convert light into electrical energy. In some kinds of light, thallium sulfide does not conduct electricity very well. But in other kinds of light, it conducts very well. Special photocells can be built to take advantage of this property. 

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