Group trends ionic radii

The radii of cations and anions derived from atoms of the main-group elements are shown at the bottom of Figure 6.13. The trends referred to previously for atomic radii are dearly visible with ionic radius as well. Notice, for example, that ionic radius increases moving down a group in the periodic table. Moreover the radii of both cations (left) and anions (right) decrease from left to right across a period. 

Inspection of the values for the entropies of hydration of the Group 2 cations in Table 2.17 shows that, with the exception of that for Be2 +, the values become less negative as the ionic radius increases. This effect is similar to that observed for the Group 1 cations. The exception of Be2+ to the general trend is possibly because of its tendency to have a tetrahedral coordination that causes it to affect fewer molecules of water in the hydration process. 

Use the Interactive Periodic Table (eChapter 5.1) to compare the atomic radius and the ionic radius of the elements in group 2A. How does the ionic radius compare to the atomic radius Explain this trend. 

Figure 7.14 (Upper) Different space groups and the types of coordination along the lanthanide series. (Middle) Plots of the SHG intensity along the type I and type II series as according to ionic radius and also (bottom) to the number of unpaired f electrons. Complexes with no unpaired f electrons are shown to follow a different trend (La, Y, Lu).

Because of the arrangement of elements on the periodic table, there are several patterns that can be seen between the elements. These patterns, or periodic trends, can be observed for atomic radius, ionic radii, ionization energies, electron affinities, and electronegativities. You should be familiar with the periodic and group trends for each of these. 

Determinations of the values of ionic radii are somewhat more complicated than those of covalent radii. Different ions formed by the same element (for example, Cu and Cu2 ) will have different radii, and it is possible that the radius of a particular ion may change slightly when surrounding groups change. Ionic radii are discussed in Chapter 12, but the trends should be noted here. 

Figure 8.9 shows the radii of ions derived from the familiar elements, arranged according to elements positions in the periodic table. We can see parallel trends between atomic radii and ionic radii. For example, from top to bottom both the atomic radius and the ionic radius increase within a group. For ions derived from elements in different groups, a size comparison is meaningful only if the ions are isoelectronic. If we examine isoelectronic ions, we find that cations are smaller than anions. For example, Na is smaller than F . Both ions have the same number of electrons, but Na... 

STEP 3 Unfold the sheet and draw lines along all fold lines. Label as follows Periodic Trends, Periods, and Groups in the first row, and Atomic Radius, Ionic Radius, Ionization Energy, and Electronegativity in the first column. 

The characteristic frequency for the CH2 groups in chelated EDTA molecules suggests that the COO groups are attached directly to the metal ion. The frequency for the CH2 group decreases generally as the ionic radius of the metal ion increases this trend is particularly true for closely similar groups of ions, for example, the alkaline earth ions or the divalent ions. 

The trend is that the smaller the ionic radius, the greater (more exothermic) is the hydration energy. One reason for this is that the water molecules can get closer to the centre of the charge so the attractive forces (ion-dipole forces) are increased. This trend can be clearly observed in group 1 elements (Table 15.3). 

The groups and periods of the periodic table display general trends in the following properties of the elements electron affinity, electronegativity, ionization energy, atomic radius, and ionic radius. 

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