Why is the second electron affinity of oxygen greater than that of sulfur? I think it should be like- second electron gain enthalpy of oxygen should be greater than the sulfur but electron affinity should be less than sulfur.

  • $\begingroup$ Electron gain enthalpy= - electron affinity $\endgroup$
    – RobChem
    Jan 12, 2015 at 14:48
  • $\begingroup$ To RobChem..may u please tell that what's exactly greater for oxgen-electron affinity or electron gain enthalpy? $\endgroup$ Jan 12, 2015 at 14:53
  • $\begingroup$ They have the same magnitude but different sign. For oxygen, the process where one electron is added to the neutral atom is exothermic so the electron gain enthalpy is negative but the electron affinity is positive. Look up the work affinity and it might help. $\endgroup$
    – RobChem
    Jan 12, 2015 at 14:55
  • $\begingroup$ I was exactly asking for the SECOND electron affinity and electron gain enthalpy between oxygen and sulphur. .. I know that second electron gain enthalpy of oxygen is greater than sulphur (with +ve sign) ..so it should have lesser electron affinity than that of sulphur (with -ve sign) ...no? $\endgroup$ Jan 12, 2015 at 15:12
  • $\begingroup$ Actually I was solving some questions and the answer given there was rather odd.. then I turned to Google but got messed up with them.. anyways ur reply is awaited and thanks for paying ur attention. .. m I right what I said just now?:) $\endgroup$ Jan 12, 2015 at 15:16

1 Answer 1


The electron affinity of an atom or molecule is defined as the amount of energy released when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion.

It is the tendency of an atom to gain electron. It is numerically equal to the negative of electron gain enthalpy.

Although fluorine has the highest electronegativity, chlorine has the highest electron affinity and this is because the considerable repulsion in the tightly packed $2p$ subshell of fluorine.

While electron gain enthalpy is enthalpy change when an isolated gaseous atom attain an electron to form a monovalent gaseous anion.

Chlorine ($\ce{Cl}$) has more negative electron gain enthalpy than fluorine the reason is same as above.


Wikipedia and chemistry reader


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