Group 1 The Alkali Metals

The alkali metals - lithium, sodium, potassium, rubidium, caesium and francium - are members of group 1 of the periodic table, and each has a ground state valence electronic configuration ns. Discussions of these metals usually neglect the heaviest member of the group, francium. The isotope Fr occurs naturally, but only as the decay product of Ac in uranium ores. The half-life of Fr is 21.8 min, and it is estimated that, at a given moment, there is 30g of francium in the Earth s cmst. Isotopes of Fr can be prepared artificially in nuclear reactions, but have no practical applications. 

We have already covered several aspects of the chemistry of the alkali metals as follows  

NaCl and CsCl structure types (Section 6.11) energetics of the dissolution of MX (Section 7.9) standard reduction potentials, m+/m (Section 8.7) energetics of MX transfer from water to organic solvents (Section 9.3)  

Potash is obtained both by underground mining and from the evaporation of natural brines as illustrated in the photograph. World production of potash rose from 0.32 Mt in 19(X) to 35 Mt in 2008, with the major producers being Canada, Russia, Belarus and Germany. About 95% of potash produced is destined for use in fertilizers. The potash market collapsed 

Major agricultural countries such as the US must import large amounts of potash to meet commercial needs. In 2008, imports of 5.8 Mt supplemented the 1.1 Mt of home-produced potash in the US. World reserves of potash are estimated to be approximately 250 billion tonnes. 

A challenge is to develop practical thermal or photochemical processes for generating hydrogen from its most abundant source—water.  

H2 is prepared industrially by cracking petroleum hydrocarbons with solid catalysts, also forming alkenes 

Molecular hydrogen is an important reagent, especially in the industrial hydrogenation of unsaturated organic molecules. Transition-metal catalyzed hydrogenations are discussed in Chapter 14. 

Alkali metal salts, in particular sodium chloride, have been used since antiquity. In early times, salt was used in the preservation and flavoring of food. However, because of the difficulty of reducing alkali metal ions, the elements were not isolated until comparatively recently. Two of the alkali metals, sodium and potassium, are essential for human life their careful regulation is important in treating a variety of medical conditions. 

Potassium and sodium were first isolated in 1807 by Davy as products of the electrolysis of molten KOH and NaOH. In 1817, Arfvedson recognized similarities between the solubilities of compounds of lithium and those of sodium and potassium. The following year, Davy also isolated lithium by electrolysis of molten Li20. Cesium and rubidium were discovered with the help of the spectroscope in 1860 and 1861, respectively they were named after the colors of the most prominent emission lines (Latin, caesius, sky blue, rubidus, deep red ). Francium was not identified until 1939 as a short-lived radioactive isotope from the nuclear decay of actinium. 

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In crystals of salts of oxygen-containing carbanions, such as [(OgN)2 C—C(N02)2]2, (2) (3), or the Meisenheimer complexes [C6H2(N02)3 (OR)(OR )]- (41), (where R and R are alkyl groups), the alkali metal is found to have oxygen neighbours from different anions there are no short M—C contacts. 

Table I lists the measured frequency changes for all of the metals we have studied. It is Interesting to compare the trends in Av2 within groups. The alkali metal interaction clearly...

We have seen that the periodic table originated as a way to portray the systematic properties of the elements. Mendeleev was primarily responsible for first showing its usefulness in correlating and predicting the elemental properties. In this section we will summarize much of the information available from the table. We will also illustrate the usefulness of the table by discussing the properties of a representative group, the alkali metals. 

As a group, the alkali metals (the Group lA elements) are the most electropositive (or the least electronegative) elements known. They exhibit many similar properties, some of which are listed in Table 20.4. From their electron configurations we expect the oxidation number of these elements in their compounds to be +1 since the cations would be isoelectronic with the noble gases. This is indeed the case. 

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