Sulphur ions, electron affinity

The electron affinity E of the halogens is indeed positive, but for oxygen and sulphur energy is necessary to form a two-fold negative ion, namely about 150 and 90 kcal/gr.atom. (Actually 71 and 48 keal/gr. atom respectively, are set free in the formation of O- and S ). The electron affinity of hydrogen is weakly positive 16.5 kcal/gr.atom are set free in the formation of H. ... 

For the elements oxygen and sulphur which form di-negative ions, the electron affinity values are negative. Although cnerg) is released when one extra electron is added, much more energy is required to force tlie second electron into an ionised atom. 

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