Trends in First Ionization Energy

Summarizing Ionization Energy for Main-Group Elements  

On the basis of periodic trends, determine which element in each pair has the higher first ionization energy (if possible). 

S has a higher ionization energy than A1 because as you trace the path between A1 and S on the periodic table, you move to the right within the same row. Ionization energy increases as you go to the right due to increasing effective nuclear charge. 

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The trends in first ionization energies, first electron attachment energies, atomic sizes and electronegativity coefficients of the elements across the groups and down the periods of the periodic classification. 

This small table provides a summary of the general trends in first ionization energies. 

General trends in first ionization energies of A group elements with position in the periodic table. Exceptions occur at Groups IIIA and VIA. 

Fig- 4 Flowchart concept map showing trend in first ionization energy across Period 3... 

Describe the trend in first ionization energies within a group. 

Describe the general trend in first ionization energies in group 2, and explain why this trend occurs. 

Knowledge Required (1) The definition of ionization energy. (2) The periodic trends in first ionization energies within groups and periods. 

A FIGURE 7.9 Trends in first ionization energies of the eiements. 

Analyze and Plan We are given the chemical symbols for five elements. To rank them according to increasing first ionization energy, we need to locate each element in the periodic table. We can then use their relative positions and the trends in first ionization energies to predict their order. 

Further exceptions to the general trend in first ionization energies occur at the low ends of Groups 13 and 14, the first ionization energies of T1 and Pb being respectively higher than those of the corresponding elements in period 5, In and Sn. Ilie exceptions are explained by relativistic effects that are dealt with in Section 4.5. 

Now let us turn our attention to the exceptions to the regular trend in first ionization energies. For example, why is the first ionization energy of A1 smaller than that of Mg and the first ionization energy of S smaller than that of P ... 

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