Problem: The electron affinity of an element is positive if energy is absorbed during the process of accepting an electron and negative if energy is released during the process. Using the electron configuration of the atom or ion undergoing the addition of an electron, predict whether the electron affinity will be positive or negative for the following reactions, and classify them accordingly.Electron affinity and electron configuration of the atoms The electron affinity of elements is a periodic property, so you can predict whether the electron affinity of an element is positive or negative based on its electron configuration. In general, you can use the following rules to correlate electron affinity and electron configuration: The addition of an electron to a neutral atom that can complete any subshell, such as an s, p, d, or f subshell, will be favorable, and the electron affinity will be negative. For example, the I atom has five electrons in the 5p subshell. The addition of an extra electron will result in a completely filled 5p subshell. The addition of an electron will be favorable, and, therefore, the electron affinity is negative.I(g) + e− → I− (g), ΔE < 0[Kr]4d105s25p5         [Kr]4d105s25p6 The addition of an electron to any negatively charged ion will need to overcome the repulsive force of the negative ion. This is generally less favorable than adding an electron to a neutral atom, and the electron affinity will be positive. Even though the additional electron will complete the octet, as in the case of an O− ion where the addition of electron will complete the 2p subshell, the electron affinity is a positive value. O− (g) + e− → O2− (g), ΔE > 01s22s22p5        1s22s22p6The addition of an electron to a neutral atom that has a completely filled subshell will result in a loss of stability associated with completely filled subshells. This process is often less favorable, and the electron affinity will be positive. For example, the Xe atom has a completely filled 5p subshell. The addition of an extra electron will be unfavorable, and, therefore, the electron affinity is positive. Xe(g) + e− → Xe− (g), ΔE > 0 [Kr]4d105s25p6       [Kr]4d105s25p66s1

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The electron affinity of an element is positive if energy is absorbed during the process of accepting an electron and negative if energy is released during the process. Using the electron configuration of the atom or ion undergoing the addition of an electron, predict whether the electron affinity will be positive or negative for the following reactions, and classify them accordingly.



Electron affinity and electron configuration of the atoms 

The electron affinity of elements is a periodic property, so you can predict whether the electron affinity of an element is positive or negative based on its electron configuration. 

In general, you can use the following rules to correlate electron affinity and electron configuration: 

  • The addition of an electron to a neutral atom that can complete any subshell, such as an s, p, d, or f subshell, will be favorable, and the electron affinity will be negative. For example, the I atom has five electrons in the 5p subshell. The addition of an extra electron will result in a completely filled 5p subshell. The addition of an electron will be favorable, and, therefore, the electron affinity is negative.

I(g) + e → I (g), ΔE < 0

[Kr]4d105s25p5         [Kr]4d105s25p6 

  • The addition of an electron to any negatively charged ion will need to overcome the repulsive force of the negative ion. This is generally less favorable than adding an electron to a neutral atom, and the electron affinity will be positive. Even though the additional electron will complete the octet, as in the case of an O ion where the addition of electron will complete the 2p subshell, the electron affinity is a positive value. 

O (g) + e → O2 (g), ΔE > 0

1s22s22p5        1s22s22p6

  • The addition of an electron to a neutral atom that has a completely filled subshell will result in a loss of stability associated with completely filled subshells. This process is often less favorable, and the electron affinity will be positive. For example, the Xe atom has a completely filled 5p subshell. The addition of an extra electron will be unfavorable, and, therefore, the electron affinity is positive. 

Xe(g) + e → Xe (g), ΔE > 0 

[Kr]4d105s25p6       [Kr]4d105s25p66s1

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