The second electron gain enthalpies (in kJ mol–1) of oxygen and sulphur respectively are:a)–780, + 590b)–590, + 780c)+590, + 780d)+780, +590Correct answer is option 'D'. Can you explain this answer?

Question

The second electron gain enthalpies (in kJ mol&#8211;1) of oxygen and sulphur respectively are:a)&#8211;780, + 590b)&#8211;590, + 780c)+590, + 780d)+780, +590Correct answer is option 'D'. Can you explain this answer?

Answer

The second electron gain enthalpy (electron affinity) is the energy released when a neutral atom gains an electron to form a negative ion with a 1- charge.

Explanation:
- Oxygen has 6 electrons in its valence shell and needs 2 more electrons to complete its octet.
- When it gains the first electron, it becomes a negatively charged ion, O-.
- However, when it gains the second electron, it has to overcome a repulsive force from the already existing negative charge. This makes it more difficult for oxygen to gain the second electron, hence it has a higher second electron gain enthalpy value.
- Sulphur, on the other hand, has 6 electrons in its valence shell and needs 2 more electrons to complete its octet.
- When it gains the first electron, it becomes a negatively charged ion, S-.
- When it gains the second electron, it is easier for sulphur to gain it as compared to oxygen, hence it has a lower second electron gain enthalpy value.

Therefore, the correct answer is option 'D' where oxygen has a higher second electron gain enthalpy of 780 kJ mol-1 and sulphur has a lower second electron gain enthalpy of 590 kJ mol-1.

Answer

The process is O(-) + e = O(2-) and S(-) +e = S(2-)  ...actually electron gain enthalpy mean generally amount of energy relish when electron add and generally it is negative because of energy relish ...but after add one electron it became more electron reach and reluctant to add electron  so 2 nd electron gain enthalpy is positive for O and S ... Now O has 2p outer orbital and S has 3p outer orbital ...Because of greater electron clouding in O(-) it more reluctant to accept electron compare to S(-) ...so D is correct

Answer

Electron gain enthalpy is negative when first electron is added to isolated gaseous atom because at this energy is released but when second electron is added it is added to an anion which is electron rich this creates a repulsive force to the incoming electron and we need to supply energy to add second electron hence second electron gain enthalpy becomes positive. Now coming towards Oxygen and sulphur according to periodic trends electron gain enthalpy decreases down the group, this is due to increase in atomic size as oxygen has less atomic size than sulphur electron experiences a greater attractive force towards nucleus while in case of sulphur atomic size is bigger and attractive force of electron towards nucleus decreases which results in decrease in repulsive force of electron. hence the amount of energy required to add an electron is lesser in sulphur than in case of oxygen.  Does option D is correct

Answer

I think it should be energy required for second electron gain enthalpy not released

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