Survey of the alkaline-earth metals

Beryllium, magnesium, calcium, strontium, barium, and radium constitute Group 2 in the Periodic Table. These elements (or simply the Ca, Sr, and Ba triad) are often called alkaline-earth metals. Some important properties of group 2 elements are summarized in Table 12.5.1. 

All group 2 elements are metals, but an abrupt change in properties between Be and Mg occurs as Be shows anomalous behavior in forming mainly covalent compounds. Beryllium most frequently displays a coordination number of four, usually tetrahedral, in which the radius of Be2+ is 27 pm. The chemical behavior of magnesium is intermediate between that of Be and the heavier elements, and it also has some tendency for covalent bond formation. 

With increasing atomic number, the group 2 metals follow a general trend in decreasing values of h and h except for Ra, whose relatively high I and h are attributable to the 6s inert pair effect. Also, high I3 values for all members of the group preclude the formation of the +3 oxidation state. 

As the atomic number increases, the electronegativity decreases. In the organic compounds of group 2 elements, the polarity of the M-C bond increases in the order 

This is due to the increasing difference between the Xs of carbon (2.54) and those of the metals. The tendency of these compounds to aggregate also increases in the same order. The BeR2 and MgR2 compounds are linked in the solid phase 

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