The Group 1 Elements Li, Na, K, Rb, Cs, Fr

The closely related elements lithium, sodium, potassium, rubidium, and cesium, often termed the alkali metals, have a single s electron outside a noble gas core. Some relevant data are listed in Table 3-1. 

As a result of the low ionization enthalpies for the outer electrons and the sphericity and low polarizability of the resulting M+ ions, the chemistry of these elements is principally that of their +1 ions. No other cations are known or, in view of the values of the second ionization enthalpies, expected. The ions M, where the s shell is filled, are discussed in Section 3-4. 

The chemistry of the elements is mainly that of ionic salts in the solid state and solvated cations. Although some lithium and even sodium compounds are soluble in organic solvents, such compounds as (LiCH3)4 have essentially ionic Li+ for sodium and potassium compounds, close ion pairing can occur, as discussed in later sections. 

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

Other ions that have chemical behavior closely resembling that of the Group 1 ions are  

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FIGURE 5.1 Agraph of atomic radius in picometers (pm) versus atomic number shows a rise-and-fall pattern of periodicity. The maxima occur for atoms of group 1A elements (Li, Na, K, Rb, Cs, Fr) the minima occur for atoms of the group 7A elements. Accurate data are not available for the group 8A elements. 

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). 

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. 

Alkali metals (2.5) Elements of Group 1, the first column of the periodic table, except hydrogen Li, Na, K, Rb, Cs, and Fr. 

Now that you know more about electronic configurations, you can better understand the periodic law and table. First, consider the electronic configurations of the elements belonging to the same group of the periodic table. Group 1A(1), for example, contains Li, Na, K, Rb, Cs, and Fr, with electronic configurations for the first four elements as shown below ... 

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 Group 1 elements—lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr)—are called the alkali metals. The alkali elements are soft, silvery-white metals and good conductors of heat and electricity. Their chemistry is relatively uncomplicated they lose their s valence electron and form a 1 + ion with the stable electron configuration of the noble gas in the preceding period. 

Figure 5.1. The graph shows a periodic rise-and-fall pattern. Beginning on the left with atomic number 1 (hydrogen), the size of the atoms increases to a maximum at atomic number 3 (lithium), then decreases to a minimum, then increases again to a maximum at atomic number 11 (sodium), then decreases, and so on. It turns out that all the maxima occur for atoms of group 1A elements—Li (atomic number, Z = 3), Na (Z = 11), K (Z = 19), Rb (Z = 37), Cs (Z = 55), and Fr (Z = 87)—and that the minima occur for atoms of the group 7A elements.

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. 

The elements in group 1 are hydrogen and the alkali metals lithium li, sodium Na, potassium K, rubidium Rb, cesium Cs and francium Fr. The last one, francium, was discovered in 1939 by Marguerite Percy in Paris. It will be described in Chapter 52 The Radioactive Elements. The others wiU be treated in this and the following two chapters. 

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