Group 2A The Alkaline-Earth Metals

Like the alkali metals, the alkaline earth metals are all solids at room temperature and have typical metallic properties (A TABLE 7.5). Compared with the alkali metals, the alkaline earth metals are harder and more dense and melt at higher temperatures. 

The first ionization energies of the alkaline earth metals are low but not as low as those of the alkali metals. Consequently, the alkaline earth metals are less reactive than their alkali metal neighbors. As noted in Section 7.4, the ease with which the elements lose electrons decreases as we move across a period and increases as we move down a group. Thus, beryllium and magnesium, the lightest alkaline earth metals, are the least reactive. 

The trend of increasing reactivity within the group is shown by the way the alkaline earth metals behave in the presence of water. Beryllium does not react with either water or steam, even when heated red-hot. Magnesium reacts slowly with liquid water and more readily with steam  

Calcium and the elements below it react readily with water at room temperature (although more slowly than the alkali metals adjacent to them in the periodic table). The reaction between calcium and water ( FIGURE 7.24), for example, is 

Equations 7.22 and 7.23 illustrate the dominant pattern in the reactivity of the alkaline earth elements They tend to lose their two outer s electrons and form 2-1- ions. For example, magnesium reacts with chlorine at room temperature to form MgCl2 and bums with dazzling brilliance in air to give MgO  

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In the next three sections we will study the chemistry of selected metals from Group 1A (the alkali metals). Group 2A (the alkaline earth metals), and Group 3A (aluminum). 

Elements in the same group of the periodic table are most likely to exhibit similar properties. We therefore expect Ca and Mg to be most alike because they are in the same group (2A, the alkaline earth metals). 

Solution (a) and F are isoelectronic anions, both containing 10 electrons. Because has only seven protons and F has nine, the weaker attraction exerted by the nucleus of makes it the larger ion. (b) Both Mg and Ca belong to Group 2A (the alkaline earth metals). Thus, Ca ion is larger than Mg " because the outer electrons in are in a larger shell (n = 3) than are the outer electrons in Mg (n = 2). 

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