# Explain why thw electron affinities of elements of period 3 are higher than corresponding elemts of period 2

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by neshu1

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by neshu1

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Similarly in the case of sulphur, while first electron gain enthalpy is negative since 200 kJ of energy is released when 1 mole of S atoms get converted to S- ions and second electron gain enthalpy is positive since 590 kJ of energy has to be supplied to convert 1 mole of S- ions to S2- ions.

Thermodynamically , the energy released is given a negative sign and energy absorbed is given a positive sign. Accordingly, when a species has a positive electron affinity , DH , accompanying the addition of an electron to the species, isnegative and if it has a negative electron affinity, DH is positive. Thus for the reaction Cl + e ® Cl- , while electron affinity is positive , while electron gain enthalpy is negative. In various calculations involving DH, the value of electron affinity of chlorine would be taken as -349 kJmol-1and not +349 kJmol-1.