Variations in Electron Attachment Energies

The values of the electron attachment energies for the elements of the second short period (Li to Ne) may be understood by the variations in nuclear charge, and in interelectronic repulsion and exchange energies 

For the carbon atom the 2p configuration has the energy Efcote) + 2 - K that of the C ion is E(core) + 3Ej - 3K the difference gives - 2K as the electron attachment energy for the carbon atom. 

Q Check the derivation of the terms in Table 4.3 for the nitrogen and oxygen atoms. 

Q Account for the first electron attachment energy of the calcium atom (+186 kJ mol ) being greater than that of the potassium atom (-48 kJ mol ). 

A An electron attaching itself to a potassium atom would occupy the 4s orbital, pairing up with the valency electron already present. There would be interelectronic repulsion between the two 4s electrons, but this is overcome by the effective nuclear charge of the K ion. In the calcium case the 4s orbital is already full, and the extra electron must find space in a 3d orbital, which is the next level of lowest energy. 

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Figure 1.4 The first ionization 1.6.2 Variations in Electron Attachment Energies...

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