Ionization energy alkaline earth metals

The chemistry of the transition metals is determined in part by their atomic ionization energies. Metals of the 3d and 4d series show a gradual increase in ionization energy with atomic number (Z), whereas the trend for the 5d series is more pronounced (Figure 20-3). First ionization energies for transition metals in the 3d and 4d series are between 650 and 750 kJ/mol, somewhat higher than the values for Group 2 alkaline earth metals but lower than the typical values for nonmetals in the p block. 

The alkaline earth metals undergo the same kinds of redox reactions that the alkali metals do, but they lose two electrons rather than one to yield dipositive ions, M2+. Because their first ionization energy is larger than that of alkali metals (Figure 6.3), the group 2A metals tend to be somewhat less reactive than alkali metals. The general reactivity trend is Ba > Sr > Ca > Mg > Be. 

Compare the alkali metals with the alkaline earth metals with respect to (a) atomic radii, (b) densities, (c) first ionization energies, and (d) second ionization energies. Explain the comparisons. 

FIGURE 8.11 Variation of the first ionization energy with atomic number. Note that the noble gases have high ionization energies, whereas the alkali metals and alkaline earth metals have low ionization energies. 

The group 2A elements (the alkaline earth metals) have higher first ionization energies than the alkali metals do. The alkaline earth metals have two valence electrons (the outermost electron confignration is ns ). Because these two s electrons do not shield each other well, the effective nuclear charge for an alkaline earth metal atom is larger than that for the preceding alkali metal. Most alkaline earth compounds contain dipositive ions (Mg +, Ca, Sr, Ba +). The Be ion is isoelectronic with Li and with He, Mg is isoelectronic with Na and with Ne, and so on. 

The elements most likely to form ionic compounds have low ionization energies (such as the alkali metals and the alkaline earth metals, which form cations) or high electron affinities (such as the halogens and oxygen, which form anions). 

---