Trends in electron affinities

The electron affinity (EA) is the energy change (in kJ) accompanying the addition of 1 mol of electrons to 1 mol of gaseous atoms or ions. As with ionization energy, there is a first electron affinity, a second, and so forth. The first electron affinity (EAi) refers to the formation of 1 mol of monovalent (1 — ) gaseous anions  

In most cases, energy is released when the first electron is added because it is attracted to the atom s nuclear charge. Thus, EA, is usually negative (just as A// for an exothermic reaction is negative). The second electron affinity (EA2), on the other hand, is always positive because energy must be absorbed 

Despite the irregularities, three key points emerge when we examine the relative values of ionization energy and electron affinity  

Reactive metals. The elements in Groups 1 A(l) and 2A(2) have low ionization energies and slightly negative (exothermic) electron affinities. Both groups lose electrons readily but attract them only weakly, if at all. Therefore, in their ionic compounds, they form positive ions. 

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EXAMPLE 1.12 Sample exercise Predicting trends in electron affinity... 

The aufbau principle must be obeyed when an electron is added to a neutral atom, so the electron goes into the most stable orbital available. Hence, we expect trends in electron affinity to parallel trends in orbital stability. However, electron-electron repulsion and screening are more important for negative ions than for neutral atoms, so there is no clear trend in electron affinities as ft increases. Thus, there is only one general pattern ... 

Describe the trends in electron affinity and electronegativity across the periodic table (Section 3.4, Problems 13-16). 

General trends in electron affinities of A group elements with position in the periodic table. There are many exceptions. 

Explain the trends in electron affinity from aluminum to chlorine (see Table 8.4). 

Trends in Atomic Size Trends in Ionization Energy Trends in Electron Affinity... 

Strategy What are the trends in electron affinity in a periodic group and in a particular period. Which of the above elements are in the same group and which are in the same period ... 

Explain the trend in electron affinities of elements in the second row (Na to Cl) of the periodic table. 

The electron affinity of a Group VA element is generally less negative than the preceding Group IVA element. Note the trend in electron affinities in the following ... 

What is the explanation for the observed trend in electron affinity in the periodic table ... 

Write a concise paragraph explaining the general trends in electron affinity. Your answer should include a definition of this property. 

New problems on explaining trends in electron affinities on the basis of radial distribution functions, the reaction between aqueous copper chloride solution and aluminum metal, assigning structural classes to simple boranes, isomers of carboranes, and semitopological diagrams for alanes... 

Figure 8.16 displays the electron affinities for a number of main-group elements. As you can see from this figure, the trends in electron affinity are not as regular as trends in other properties we have examined. For instance, we might expect electron affinities to... 

Most groups (columns) of the periodic table do not exhibit any definite trend in electron affinity. Among the group lA metals, however, electron affinity becomes more positive as we move down the column (adding an electron becomes less exothermic). 

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