Actinium, properties

Name from protos (Greek = first) i.e., before actinium Properties... 

URANIUM compounds), Pb from the thorium series, and Pb from the actinium series (see Actinides and transactinides). The crystal stmcture of lead is face-centered cubic the length of the edge of the cell is 0.49389 nm the number of atoms per unit cell is four. Other properties are Hsted in Table 1. 

The isolation and identification of 4 radioactive elements in minute amounts took place at the turn of the century, and in each case the insight provided by the periodic classification into the predicted chemical properties of these elements proved invaluable. Marie Curie identified polonium in 1898 and, later in the same year working with Pierre Curie, isolated radium. Actinium followed in 1899 (A. Debierne) and the heaviest noble gas, radon, in 1900 (F. E. Dorn). Details will be found in later chapters which also recount the discoveries made in the present century of protactinium (O. Hahn and Lise Meitner, 1917), hafnium (D. Coster and G. von Hevesey, 1923), rhenium (W. Noddack, Ida Tacke and O. Berg, 1925), technetium (C. Perrier and E. Segre, 1937), francium (Marguerite Percy, 1939) and promethium (J. A. Marinsky, L. E. Glendenin and C. D. Coryell, 1945). 

Brdnsted-Lowry theory, 194 contrast definitions, 194 indicators, 190 reactions, 188 titrations, 188 Acids, 183 aqueous, 179 carboxylic, 334 derivatives of organic, 337 equilibrium calculations, 192 experimental introduction, 183 names of common, 183 naming of organic, 339 properties of, 183 relative strengths, 192, 451 strength of, 190 summary, 185 weak, 190, 193 Actinides, 414 Actinium... 

It was first identified and named brevium, meaning brief, by Kasimir Fajans and O. H. Gohring in 1913 because of its extremely short half-life. In 1918 Otto Hahn (1879—1968) and Lise Meitner (1878-1968) independently discovered a new radioactive element that decayed from uranium into (actinium). Other researchers named it uranium X2. It was not until 1918 that researchers were able to identify independently more of the elements properties and declare it as the new element 91 that was then named protactinium. This is another case in which several researchers may have discovered the same element. Some references continue to give credit for protactinium s discovery to Frederich Soddy (1877—1956) and John A. Cranston (dates unknown), as well as to Hahn and Meitner. 

These two kinds of lead are now known to be isotopes, or inseparable elements which belong in the same space in the periodic table and yet differ in atomic weight and in radioactive properties. According to Frederick Soddy, the first clear recognition of isotopes as chemically inseparable substances was that of H. N. McCoy and W. H. Ross in 1907 (75,107). Strictly speaking, the science of radioactivity has revealed only five naturally occurring new elements with distinctive physical and chemical properties polonium, thoron, radium, actinium, and uranium X2. All the other natural radioactive elements share previously occupied places in the periodic table. 

The properties of this new element left no doubt that it was the missing alkali, eka-cesium, number 87. In 1946 Mile. Perey suggested that the name actinium K be kept for the naturally occurring isotope which resulted from the decay of actinium, but that element 87 in general... 

The failure to discover francium earlier is easy to understand when it is remembered that the half-life of the longest lived isotope is only 21 minutes. This gives the element the distinction of being the most unstable to radioactive disintegration of all elements up to number 98 (38). It is also noteworthy that this is the only element in the group discussed in this chapter which was not discovered by artificial preparation in the laboratory. Nevertheless, the rarity of actinium in nature is so great that this element is best prepared artificially when its properties or those of its daughter elements are to be studied. 

The seventh-period inner transition metals are called the actinides because they fall after actinium, Ac. They, too, all have similar properties and hence are not easily purified. The nuclear power industry faces this obstacle because it requires purified samples of two of the most publicized actinides uranium, U, and plutonium, Pu. Actinides heavier than uranium are not found in nature but are synthesized in the laboratory. 

Elements 43, Masurium 61, Illinium 84, Polonium or Radium F 89, Actinium 91, Uranium Xs do not appear in the atomic weight tables. Although their existence has been indicated by means of X-rays or radioactive properties, they have not been isolated in amounts to allow of atomic weight determination. 

A comparison of some properties of Sc and Y with those of Lu and La is given in Table 2.5. All these properties favour the placement of lutetium and lawrencium, rather than lanthanum and actinium in group III B. 

It should be noted that although for decennia lanthanum and actinium could be found below yttrium in most periodic tables, some authors have placed lutetium below yttrium in the past. For instance, in the periodic table of Werner (1905a,b), there is an open place below yttrium at the position where lutetium is expected, but it should be realized that at that time lutetium had not yet been discovered (this was in 1907). However, Werner did not consider lanthanum as a homologue of yttrium, because of the differences in chemical properties between these two elements. Also in the circular system of Janet (Figure 28), the left-step table of Janet (Figure 32) and in the periodic table of Bohr (Figure 21), lutetium was placed below yttrium. 

Actinium has chemical properties like those of lanthanum (number 57), the element just above it in the periodic table. Actinium is also similar to radium, the element just before it (number 88) in Row 7. 

Only limited information is available about actinium. It is known to be a silver metal with a melting point of 1,920°F (1,050°G) and a boiling point estimated to be about 5,800°F (3,200°C). The element has properties similar to those of lanthanum. Generally speaking, elements in the same column in the periodic table have similar properties. Few compounds of actinium have been produced. Neither the element nor its compounds have any important uses. 

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). 

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