Properties of the alkali metals

The Group 1 elements are soft, low-melting metals which crystallize with bee lattices. All are silvery-white except caesium which is golden yellow - in fact, caesium is one of only three metallic elements which are intensely coloured, the other two being copper and gold (see also pp. 112, 1177, 1232). Lithium is harder than sodium but softer than lead. Atomic properties are summarized in Table 4.1 and general physical properties are in Table 4.2. Further physical properties of the alkali metals, together with a review of the chemical properties and industrial applications of the metals in the molten state are in ref. 11. 

All the alkali metals have characteristic flame colorations due to the ready excitation of the outermost electron, and this is the basis of their analytical determination by flame photometry or atomic absorption spectroscopy. The colours and principal emission (or absorption) wavelengths, X, are given below but it should be noted that these lines do not all refer to the same transition for example, the Na D-line doublet at 589.0, 589.6 nm arises from the 3s — 3p transition in Na atoms formed by reduction of Na+ in the flame, whereas the red line for lithium is associated with the short-lived species LiOH. 

Colour X/nm Crimson 670.8 Yellow 589.2 Violet 766.5 Red-violet 780.0 Blue 455.5 

The reduction potential for lithium appears at first sight to be anomalous and is one of the 

Estimates of the heat of hydration of Li+(g) give values near 520kJ mol compared with 

6 nm arises from the 3s — 3p transition in Na atoms formed by reduction of Na in the flame, whereas the red line for lithium is associated with the short-lived species LiOH. 

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A signiflcairt property of the alkali metal halides is the solubility of the metals in their molten halides. Typical values of the consolute temperatures of metal-chloride melts are 1180°C in Na-NaF, 1080°C in Na-NaCl, 790°C... 

As in the discussion of hydrogen, in this section we examine the properties of the alkali metals in the context of the periodic table and focus on significant applications of the elements and selected compounds. The valence electron configuration of the alkali metals is s1, where n is the period number. Their physical and chemical properties are dominated by the ease with which the single valence electron can be removed (Table 14.3). 

R. W. Ohse, ed.. Handbook of Thermodynamic ami Transport Properties of the Alkali Metals lUPAC, Blackwell Scientific Publications, Oxford, 1985. 

The properties of the alkali metals and of their salts are roughly functions of the at. wt. of the metals. There is generally a break in the curve about potassium so that lithium and sodium form one series, and potassium, rubidium, and caesium another. The properties of the series, K, Rb, Cs generally change more regularly than the series Li, Na, K, although some irregularities do occur—e.g. the m.p. of the nitrates. 

TAB1JE 14.4 Chemical Properties of the Alkali Metals Reactant Reaction with alkali metal (M)... 

Look at the properties of the alkali metals summarized in Table 6.4, and predict reasonable values for the melting point, boiling point, density, and atomic radius of francium. 

Look up the physical and chemical properties of the alkali metals. 

This exercise should help you learn certain key properties of the alkali metals, and help develop the skills of predicting the properties of unfamiliar elements from the features of those that you have learnt. 

The structures and properties of the alkali metal oxides are summarized in Table 12.2.1. 

The ionic hydrides are white solids with high melting points, and all of the alkali metal hydrides have the sodium chloride crystal structure. Because they resemble the salts of the alkali and alkaline earth metals, the ionic hydrides are often referred to as saline or salt-like hydrides. The properties of the alkali metal hydrides are shown in Table 6.3, and those of the alkaline earth hydrides are shown in Table 6.4. 

Lithium is a weak donor. It leads to the generation of only low radical concentrations where intramolecular combinations (cyclization) predominate. With increasing donor properties of the alkali metal, the generation of anion radicals is accelerated and their concentration increases. The probability of intermolecular reactions increases and more oligomers and polymers are formed. 

Table 10. Some properties of the alkali metal cations [94]...

Fundamental atomic and physical properties of the alkali metals are given in Tables 1, 2, and 3. The elements are characterized by having electron configurations each with a single s orbital electron outside a noble gas core (see Table 1). Sodium and cesium are mononucUdic so that their relative atomic masses are known extremely accurately in effect, the same can be written for potassium and rubidium since their isotopes (of which there are three and two, respectively) have... 

TABLE 18.4 Selected Physical Properties of the Alkali Metals... 

E. E. Shpil rain, K. A. Yakimovich, et al., "Thermophysical Properties of the Alkali Metals", STANDARDS, Moscow, 1970. 

Some of the physical properties of the alkali metals are listed in Table 3. All these elements are so soft that they can be easily cut with a knife. The freshly cut surface of an alkali metal is shiny, but it dulls quickly as the metal reacts with oxygen and water in the air. Like other metals, the alkali metals are good conductors of electricity. 

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