The first electron affinity for oxygen is +141 kJ/mol while the second electron affinity is -780 kJ/mol. Briefly account for the difference in magnitude and sign for these two values.
The Correct Answer and Explanation is:
The first electron affinity of oxygen is +141 kJ/mol, which means that energy is released when an electron is added to an oxygen atom. This is because the oxygen atom, with its relatively high electronegativity, attracts the added electron, and the process is exothermic (releases energy).
However, the second electron affinity is -780 kJ/mol, which is a significantly larger negative value. This indicates that the process of adding a second electron is endothermic, requiring energy to be absorbed rather than released. This occurs because after the first electron is added, the oxygen ion (O⁻) now has a negative charge. As a result, the added electron experiences a repulsive force from the already negatively charged ion. The electron-electron repulsion increases the energy required to add another electron.
In summary, the difference in magnitude and sign between the first and second electron affinities reflects the nature of the interaction between the electron and the atom. The first electron affinity is exothermic because of the attractive force between the oxygen atom and the added electron. The second electron affinity is endothermic due to the increased repulsion between the negative charge of the oxygen ion and the additional electron, requiring energy input for the process to occur.
