Francium abundance

Radon, the heaviest of the noble gases, has been much publicized in recent years because of a fear that low-level exposures increase the risk of cancer. Like astatine and francium, its neighbors in the periodic table, radon is a radioactive element with only a minute natural abundance. It is produced by radioactive decay of the radium present in small amounts in many granitic rocks, and it can slowly seep into basements, where it remains unless vented. If breathed into the lungs, it can cause radiation damage. 

Because of its extremely low abundance, short half-life, and high radioactivity, neither francium nor its compounds have economic applications. see also Alkali Metals Curie, Marie Sklodowska Mendeleev, Dimitri Radioactivity. 

Li, Rb and Cs are of lower abundance and are obtained from silicate minerals. Francium (Fr) is a radioactive element and occurs in very small quantities in uranium minerals. The longest-lived isotope of francium is 223Fr (ty2 = 22 min). 

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). 

Only sodium and potassium are moderately abundant on Earth, and are major elements of life (see Topic J3 ). They occur in many silicates, but weathering reactions at the Earth s surface lead to the dissolution of the very soluble cations, which are common in sea water and are eventually deposited in halide minerals such as NaCl and KC1 (see Topic J2). Li, Rb and Cs are of lower abundance, and obtained from silicate minerals. Francium is radioactive. Its longest-lived isotope Fr has a half-life of only 22 min and occurs in exceedingly small amounts in uranium minerals (see Topics AT,... 

An asterisk denotes a radioactive isotope whose lifetime is indicated in the column Natural abundance. When a stable element has several radioactive isotopes, a few ones have been chosen for their interest in different applications. For the radioactive elements, only the isotopes with the longest lifetimes and at least one with a nonzero nuclear spin I are indicated. The electronic configuration of an element with atomic number Z is given in italics in the Name and symbol column. When relevant, the old Group label notation of the periodic table is indicated in brackets in this same column. The radioactive elements francium, radium, and actinium (Z = 87, 88, and 89, respectively) have been omitted. 

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. 

Rubidium, cesium (spelled caesium in England), and francium are soft, silvery gray metals. The abundances of these three elements are far less than the abundances of lithium, sodium, and potassium. The following is a list of three notable characteristics of these elements ... 

Sodium and potassium are abundant in Earth s crust, each comprising about 2.5 percent, and the two being the 6th and 7th most abundant elements, respectively. Other alkafi metals are at least one hundred times less abundant. Francium is virtually nonexistent in the environment since all isotopes are radioactive with short half-lives. 

The alkali metals are represented by the six chemical elements of group 1A(1) of Mendeleev s periodic chart. These six elements are, in order of increasing atomic number, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). The name alkali metals comes from the fact that they form strong alkaline hydroxides (i.e., MOH, with M = Li, Na, K, etc.) when they combine with water (i.e., strong bases capable of neutralizing acids). The only members of the alkali metal family that are relatively abundant in the Earth s crust are sodium and potassium. Among the alkali metals only lithium, sodium, and, to a lesser extent, potassium are widely used in industrial applications. Hence, only these three metals will be reviewed in detail in this chapter. Nevertheless, a short description of the main properties and industrial uses of the last three alkali metals (i.e., Rb, Cs, and Fr) will be presented at the end of the section. Some physical, mechanical, thermal, electrical, and optical properties of the five chief alkali metals (except francium, which is radioactive with a short half-life) are listed in Table 4.1. 

Values for the abundance of the element in the earth s crust and in sea are reported in many publicahons and different values are quoted for the same element. This book uses values from CRC Handbook of Chemistry and Physics [1.2]. These values are collected in Tables 1.6a and 1.6b, and the elements are ranked in order of abundance in the earth s crust. Oxygen, silicon, aluminum, iron and calcium are the most abundant elements and are ranked 1-5. Two elements with the same abundance, as for instance gallium and nitrogen, have both been given the ranking 34-35. For technetium, promethium, francium and astahne no abundance values are available and all four are ranked 89-92. 

The high sensitivity of the photoionization method is very useful for the spectroscopy of very rare elements whose spectral properties are not well known. One such element is francium (Fr), the natural abundance of which is extremely low (1 Fr atom is found in 3 X 10 atoms of natural uranium), and which is formed as a result of the decay of In our experiments (Andreyev et al. 1987, 1988), the resonance photoionization technique was used to detect Fr atoms and study their Rydberg states. The atoms... 

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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