The Anomaly of Lithium

Organic chemists have synthesized and used a large number of compounds having an alkali-metal atom bonded to one carbon atom of an organic group. Typical examples are  

The carbon-metal bond in such compounds can range from an almost completely ionic bond to one that is predominantly covalent. Benzyl-sodium, for example, may be dissolved in ether to yield a conducting solution on the other hand, the lithium-carbon bond in the colorless ethyliithium is quite nonpolar. The chemistry of such compounds, be they ionic or covalent, is best understood by considering them as sources of the highly basic carbanions that would be formed by removal of the metal ion thus the chemistry of benzylsodium is the chemistry of the CeH CH ion, whereas the chemistry of ethyliithium is the chemistry of the ethide ion, C2H Such ions will attack acidic hydrogens to form the parent hydrocarbons, will attack the more positive end of a double bond, and can carry out a number of nucleophilic displacements these reactions are discussed in texts on organic chemistry. 

The first is that in every nontransition family, in the Periodic Table, 

Second, certain elements resemble the element at their lower right or their upper left in the Periodic Table more than their own congeners. This diagonal relationship is best considered for the following portion of the table  

Beryllium and aluminum show a similar relationship. Here, the ionic radius of aluminum (0.50 A) is considerably greater than that of beryllium (0.31 A), but the charge-per-unit-size values for the two ions are quite close since the charge ratio is 3/2. This time, in situations in which size-to-charge ratio is an important consideration, beryllium and aluminum should behave similarly. (Thus the major difficulties in the early preparation of beryllium compounds were not in their separation from their homologs but rather in their separation from the corresponding aluminum compounds.) 

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