The Group I Elements Li, Na, K, Rb, Cs

The closely related elements Li, Na, K, Rb and Cs, often termed the alkali metals, have a single s electron outside a noble-gas core. Some relevant data are listed in Table 6-1. 

Element Electronic configur- ation Metal radius (A) Ionization potentials, eV M.p. CC) B.p. rc Eoa (V) P.. b - -diss (kJ mol-1) 

The low ionization potentials for the outer electrons and the fact that the resulting M+ ions are spherical and of low polarizability have as a result that the chemistry of these elements is essentially that of their +1 ions. No other oxidation state is known, nor is any to be expected in view of the magnitudes of the second ionization potentials. 

The element francium is formed in the natural radioactive decay series and in nuclear reactions. All its isotopes are radioactive with short half-lives. Precipitation reactions and solubility and ion-exchange studies have shown that the ion behaves as would be expected from its position in the group. 

Lithium has some chemical behavior that resembles the chemistry of Mg. Anomalous properties of Li result mainly from the small size of the atom and the ion the polarization power of Li+ is the greatest of all the alkali metal ions and leads to a singularly great tendency toward solvation and covalent bond formation. There is also evidence to suggest that lithium bonds comparable with hydrogen bonds exist in, e.g., H—F---Li—F and (LiF),.1 

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S-block elements The elements of the first two groups of the periodic table i.e. group 1 (H, Li, Na, K, Rb, Cs, Fr) and group 2 (Be, Mg, Ca, Sr, Ba, Ra). They are so called because their outer shells have the electronic configurations ks or ksA The s-block excludes those with inner (k - l)d levels occupied (i.e. it excludes transition elements, which also have s and occasionally s configurations). 

Elements are often referred to collectively by their periodic table group number (Group 1 A, Group 2 A, and so on). For convenience, however, some element groups have been given special names. The Group lA elements, with the exception of H (i.e., Li, Na, K, Rb, Cs, and Fr), are called alkali metals, and the... 

The elements of group I (Li, Na, K, Rb, Cs, Fr) are collectively known as alkali metals. They occur in nature only as +1 ions. They are the most electropositive in nature and their compounds are most ionic. The salts of alkali metals are quite soluble in water and thus they are found in large quantities in water and salt deposits which have formed by the evaporation of brine. However many in soluble clays also contain alkali metals as complex metal silicates. 

In August 1869 Mendeleeff presented to the Second Congress of Russian Naturalists in Moscow a communication on The Atomic Volumes of the Simple Bodies this was printed in the Transactions (pp. 62-71) and contains a periodic table in the modern form, as far as the elements whose atomic weights were well established is conceriied, and also the triads of transitional elements. In this table the groups are not separated, e.g. group I contains Li, Na, K, Cu, Rb, Ag, Cs, and group II Be, Mg, Ca, Zn, Sr, Cd, Ba. 

Monatomic ions of main-group elements have the same ionic charge the alkali metals—Li, Na, K, Rb, Cs, and Fr—form ions with a 1-h charge the halogens—F, Cl, Br, and I—form ions with a 1 - charge and so forth. 

Equation 2.4 includes m only imphcitly through (a generally weak) dependence of Ko on m. This pattern is well illustrated by Group I element ions in noble gases—a set of homologues historically used as model systems for ion transport research, for which K(E/N) have been probed extensively in experiment and theory. For example, A o(O) in He are 23, 22, 21, 20, and 18 cm /(V s) for Li, Na+, Rb+, and Cs+, respectively the values in the series decrease by just 20% despite a 19-fold mass increase.By Equation 2.4, (E/N)c for Cs in He should exceed that for Li by 25% versus 50% for measured (E/N)c that increases in the above series from 10 Td for Li+ to 15 Td for Cs" " (Figure 2.3). In this case, all ions had m>M,... 

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. 

Alkali metals are the six elements that comprise Group I in the Periodic Table lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). Especially when dissolved in water, these elements form strong bases (alkalis) capable of reacting with and neutralizing strong acids. 

Some elements from groups lA (Li, Rb, Cs) and IIA (Be, Sr, Ba) are not major bioelements and are therefore removed, even though they can be accumulated by bacteria (e.g., Cs(I) Siegel etal. 2002, Ivshina etal. 2002), or may have some biological effect (e.g., lithium) on mood disorder (Patel et al. 2002, Serretti et al. 2002) or on Mg(II)-depen-dent reactions (Ryves etal. 2002) (e.g., Be(II)). The chemical performance of these elements is matched by the more abundant macroelements Na, K, Mg, or Ca. 

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