Francium, discovery

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). 

The alkali metals form a homogeneous group of extremely reactive elements which illustrate well the similarities and trends to be expected from the periodic classification, as discussed in Chapter 2. Their physical and chemical properties are readily interpreted in terms of their simple electronic configuration, ns, and for this reason they have been extensively studied by the full range of experimental and theoretical techniques. Compounds of sodium and potassium have been known from ancient times and both elements are essential for animal life. They are also major items of trade, commerce and chemical industry. Lithium was first recognized as a separate element at the beginning of the nineteenth eentury but did not assume major industrial importance until about 40 y ago. Rubidium and caesium are of considerable academic interest but so far have few industrial applications. Francium, the elusive element 87, has only fleeting existence in nature due to its very short radioactive half-life, and this delayed its discovery until 1939. 

Francium - the atomic number is 87 and the chemical symbol is Fr. The name derives from the country France , where the French physicist Marguerite Percy from the Curie Institute in Paris, France discovered it in 1939 in the alpha particle decay of actinium, Ac => He => Fr, which was known as actinium-K and has a half-life of 22 minutes. An earlier claim of discovery in 1930 with the element name Virginium was determined to be incorrect. A similar claim for discovery of the element with atomic number 87 and named moldavium was also determined to be incorrect. The longest half-life associated with this unstable element is 22 minute Fr. 

Marguerite Catherine Perey, an assistant to Marie Curie, is credited with the discovery of francium-223 in 1939. Perey discovered the sequence of radioactive decay of radium to actinium and then to several other unknown radioisotopes, one of which she identified as francium-223. Since half of her sample disappeared every 21 minutes, she did not have enough to continue her work, but a new element was discovered. 

The element francium is named for the country of France and its most stable isotope is known as actinium K. Dimitri Mendeleev assigned it the name eka-cesium prior to its actual discovery, although at this time it was also known as russium, virginium, and moldavium. Marguerite Perey, a one-time assistant of Marie Curie, discovered francium in 1939. It is not found in its elemental state and less than one ounce is thought to exist in Earth s crust at any one time. 

The heaviest natural element is uranium, number 92. But gaps in the Periodic Table of 1925 reveal four elements not accounted for. These four missing elements are numbers 43, 61, 85, and 87, now known as technetium, promethium, astatine, and francium. Some of them were reportedly discovered before 1937, but these "discoveries proved to have been erroneous. 

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. 

A considerable extension of the ABMR measurements in the alkali elements, discussed above, was obtained by the introduction of the atomic-beam laser experiments at ISOLDE. With this method the nuclear quadrupole moments could be reached by studying the hfs of the excited state, as well as the IS in the isotopic sequences studied. A number of nuclear spins and magnetic dipole moments was also added. Of particular importance was the discovery of the Dj optical line in francium which opened the way to hfs and IS measurements in this element. The atomic-beam laser spectroscopy works at ISOLDE on the alkali elements 3,Rb, 55CS and Fr have been presented in Refs. [20-25]. 

Element 43 technetium (Tc, discovered 1939) 61, promethium (Pm, 1945) 75, rhenium (Re, 1925) 85, astatine (At, 1940) 87, francium (Fr, 1939). Lewis book was quite up-to-date— Hafnium (Hf) was discovered in 1923, the year White Lightning was published, and one can imagine the author happily updating the title of Chapter 72 in the galley proofs. Chapter 86 is titled Niton (now Radon) Chapter 91 is titled Brevium (now Protactinium). For a brief table on the discovery of the chemical elements, see A.J. Ihde, The Development of Modern Chemistry, Harper Row, New York, 1964, pp. 747-749. 

The only remaining path to success was synthesis but it proved very difficult. More than ten years passed after the discovery of Perey when francium isotopes were artificially synthesized. The nuclear reaction giving rise to the... 

Thirteen neptunium isotopes are currently known. One of them (neptunium-237) was found in 1952 in nature. This is another example when a previously synthesized element was found in nature and for which two discovery dates can be given (as for technetium, promethium, astatine, and francium). 

The third place is held by France where fifteen elements were discovered chromium (1797), beryllium (1798), boron (1808), iodine (1811), bromine (1826), gallium (1875), samarium (1879), gadolinium (1886), dysprosium (1886), radium (1898), polonium (1898), actinium (1899), europium (1901), lutecium (1907), francium (1939). It is not surprising that the radioactive elements polonium, radium, and actinium were discovered by French scientists. These discoveries proceeded from the pioneering studies of radioactivity conducted in France. A brilliant spectral analyst P. Lecoq de Boisbaudran discovered by means of spectral analysis four new elements—gallium and three rare-earth elements (samarium, gadolinium, and dysprosium). Chromium and beryllium were discovered by L. Vauquelin who was such a skillful analytical chemist that it would be unjust if he had not given the world at least one new element. 

Elements 85 and 87 fall into the region covered by the natural decay series and could therefore be expected to be fed by rare decay branches. As early as 1914, a particles were observed in carefully purified Ac (Z = 89), which implied the formation of element 87 (Meyer et al. 1914). However, the work of Marguerite Perey in 1939 is credited with the discovery of element 87 - the last discovery of a new element in nature (Perey 1939a, b). She proved that a 21 min P emitter ( 87) growing from Ac had chemical properties akin to cesium, and named the element francium (Fr). Element 85, astatine (At), the heaviest known halogen, was first produced artificially in 1940 as 85 (Ty2 = 7 h) by (a,2n) reaction on ° Bi (Corson et al. 1940a, b) before short-lived isotopes were found also in rare branches of the decay series. 

We now start a systematic chapter-by-chapter study of the eight groups of representative elements. In each of these chapters our aim is to discuss the history of the discovery of the elements, how our developing network can be applied to predict and rationalize the chemistry of the group, and what special characteristics and practical applications these elements have. We will also explore at least one special topic in depth for each group. In this chapter we discuss the alkali metals (lithium, sodium, potassium, rubidium, cesium, and francium) and add a seventh component (a knowledge of reduction potentials) to the network. The special topic in depth is liquid ammonia solutions of the Group lA and 2A metals. 

As Table 21.1 indicates, the group 1 elements, the alkali metals, are relatively abundant. Some of their compounds have been known and used since prehistoric times. Yet these elements were not isolated in pure form until about 200 years ago. The compounds of the alkali metals are difficult to decompose by ordinary chemical means, so discovery of the elements had to await new scientific developments. Sodium (1807) and potassium (1807) were discovered through electrolysis. Lithium was discovered in 1817. Cesium (1860) and rubidium (1861) were identified as new elements through their emission spectra. Francium (1939) was isolated in the radioactive decay products of actinium. 

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