Alkali metals radioactive isotopes

Rubidium, an alkali element, was discovered in the mineral water of the Max spring of what is today Bad Diirkheim, Germany, and in the mineral lepidolite (1% Rb). It is a soft, highly reactive metal with a silvery luster, and has chemical properties typical of an alkali metal. The isotopic composition of natural rubidium is 72.15% Rb, a stable isotope, and 27.85% Rb, a (3 emitter. Eighteen artificial isotopes are known (Lenk 2002). Rb changes into Sr. All rubidium salts and rubidium-containing minerals are radioactive and contain Sr, and this natural radioactivity is used for the determination of age in rocks and minerals. 

Francium s atoms are the largest and heaviest of the alkali metals in group 1 (lA). It is located just below cesium on the periodic table, and thus it is assumed to be an extremely reactive reducing agent even though it is the most scarce of the alkali metals. Its most stable isotope (Fr-223) exists for about 21 or 22 minutes. No one has figured out how to refine francium from natural minerals (ores) because the atoms of the most stable isotope found in nature (Fr-223) are scattered very thinly over the Earth s crust. All of the other 30 isotopes are produced for study by nuclear decay of other radioactive elements. 

Symbol Rb atomic number 37 atomic weight 85.468 a Group I (Group 1) alkali metal element electron configuration [Kr] 5si valence -i-l atomic radius 2.43A ionic radius, Rb+ 1.48A atomic volume 55.9 cc/g-atom at 20°C ionization potential 4.177 V standard electrode potential Rb+ + e Rb, E° = -2.98V two naturally-occurring isotopes, Rb-85 (72.165%) and Rb-87 (27.835%) Rb-87 radioactive, a beta emitter with a half-bfe 4.88xl0i° year twenty-seven artificial radioactive isotopes in the mass range 74—84, 86, 88-102. 

Symbol Na atomic number 11 atomic weight 22.9898 a Group lA (Group 1) alkali metal element electron configuration [NejSs valence +1 atomic radius 1.85A ionic radius, Na" in crystals 1.02A (for a coordination number 6) ionization potential 5.139 eV standard electrode potential, E°(Na+ + e Na) -2.71 V one naturally-occurring stable isotope, Na-23 (100%) sixteen artificial radioactive isotopes in the mass range 19-22, 24—35 longest-lived radioisotope, Na-22, ti/2 2.605 year shortest-lived isotope Na-35, ti/2 1.5 ms. 

Radioactive waste from certain nuclear power plants and from weapons testing can lead to health problems. For example, ions of the radioactive isotope strontium-90, an alkali metal, exhibit chemical behaviour similar to calcium ions. This leads to incorporation of the ions in bone tissue, sending ionizing radiation into bone marrow, and possibly causing leukemia. Given the following equation for the decay of strontium-90, how would you complete it ... 

CAS 7440-09-7. K. Metallic element of atomic number 19, group IA of the periodic table, an alkali metal, aw 39.098, valence of 1. Potassium-40 is a naturally occurring radioactive isotope. There are also two stable isotopes. The synthetic isotope, po-tassium-42, is used in tracer studies, primarily in medicine. An essential element in plant growth and in animal and human nutrition occurs in all soils. 

The alkali metals are not found free in nature, because they are so easily oxidized. They are most economically produced by electrolysis of their molten salts. Sodium (2.6% abundance by mass) and potassium (2.4% abundance) are very common in the earth s crust. The other lA metals are quite rare. Francium consists only of short-lived radioactive isotopes formed by alpha-particle emission from actinium (Section 26-4). Both potassium and cesium also have natural radioisotopes. Potassium-40 is important in the potassium-argon radioactive decay method of dating ancient objects (Section 26-12). The properties of the alkali metals vary regularly as the group is descended (Table 23-1). 

The alkaline earth metals show a wider range of chemical properties than the alkali metals. The IIA metals are not as reactive as the lA metals, but they are much too reactive to occur free in nature. They are obtained by electrolysis of their molten chlorides. Calcium and magnesium are abundant in the earth s crust, especially as carbonates and sulfates. Beryllium, strontium, and barium are less abundant. All known radium isotopes are radioactive and are extremely rare. 

The three remaining alkali metals Rb, Cs, and Fr have no biological relevance, although, as we will see in Chapter 23, the radioactive isotope of Cs, Cs, was a major pollutant after the 1986 nuclear disaster at... 

The last element in Group 1, francium, is the heaviest of the alkali metals. It is also one of the most unstable elements, and is produced by the radioactive decay of two other elements, uranium and thorium. Although there are 30 known isotopes of this metal, only one of them, francium-223, exists in nature. The remaining isotopes are produced in nuclear reactors and are too unstable to be studied at... 

Chapter 4 examines the heavier alkali metals—rubidium, cesium, and francium. Francium is a radioactive, rare element its longest-lived isotope has a half-life of only 22 minutes. The relative abundances of rubidium and cesium are much less than the abundances of lithium, sodium, or potassium, yet rubidium and cesium find important applications in atomic clocks and laser technology. 

The last discovery of an alkali metal occurred almost 80 years later. In 1939, Parisian physicist Marguerite Perey (1909-75) observed an unusual rate of radioactive decay in a sample of a salt of actinium (element 89). She managed to isolate the new element, showed that it was an alkali metal, and named it francium in honor of her native country, France. Because francium s longest-lived isotope has a half-life of only 21 minutes, francium is the rarest element below element 98 in the periodic table, which explains why francium was discovered much later than the other radioactive elements in that part of the table. 

The alkaline earth metals are somewhat less electropositive and less reactive than the alkali metals. Except for the first member of the family, beryllium, which resembles aluminum (a Group 3A metal) in some respects, the alkaline earth metals have similar chemical properties. Because their ions attain the stable electron configuration of the preceding noble gas, the oxidation number of alkaline earth metals in the combined form is almost always +2. Table 20.5 lists some common properties of these metals. Radium is not included in the table because all radium isotopes are radioactive and it is difficult and expensive to study the chemistry of this Group 2A element. 

Rubidium. Rb at. wt 85.4678 at. no. 37 valence l. Alkali metal. Widely distributed in very small quantities in earth s crust 0.0034% by wt. Natural isotopes 85 (72.15%) 87 (27.85%) Rb is radioactive Tw 4.8 X 10 years isotopes range in mass number from 79 to 95. Found with other alkali metals in rhodizite (borate), lepidolite (aluminosilicate), rubidium camallite (chloride) in sea water in mineral springs and salt lakes. Discovered by Bunsen and Kirchhoff in 1861. Frepn Hackspill, Heh. Chim. Acta II, 1003 (1928), Review Whaley, "Sodium, Potassium, Rubidi-am. Cesium and Francium in Comprehensive Inorganic Chemistry vol. I, J. C, Bailar Jr- et of.. Eds. (Pergamon Press, Oxford, 1973) pp 369-529 F. B. White, W. G. Lidman in Kirk-Othmer Encyclopedia of Chemical Technology vol 20 (Wiley-Intersdence, New York, 3rd ed., 1982) pp 492-499. 

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