Question

When the first electron gain enthalpy ( ${\Delta _{eg}}H$) of oxygen is\[ - 14kJ/mol\], its second electron gain enthalpy is:
A.Almost the same as that of the first
B.Negative, but less negative than the first
C.A positive value
D.A more negative value than the first

Answer 1

Hint: Electron gain enthalpy is defined as the amount of energy released during the addition of an electron to an isolated gaseous atom. During the addition of electron energy can either be absorbed or released.

Complete answer:
When an electron is added to a neutral gaseous atom to convert it into a negative ion. The energy change during the process is known as electron gain enthalpy. The second electron gain enthalpy is mainly positive. The half or full-filled orbitals elements are more stable and they do not accept an electron easily. Thus, it needs more energy. Therefore, when an electron is added to an isolated oxygen atom then it forms a uni-negative ion. If one more electron has to be added to a uni-negative ion, it will experience a repulsive force. Hence, more energy is needed for the addition of an electron. If it needs $2$ more electrons to complete the valence orbital to become stable. It is known as a divalent atom.

Additional Information:
 When we add an electron to the $O$ atom, it is an exothermic reaction. Thus the enthalpy is negative and when an electron is added to ${O^ - }$, it is an endothermic reaction. Thus the enthalpy is positive.

Note:
Exception in electron gain enthalpy- Chlorine has a higher negative electron gain enthalpy in the case of chlorine and fluorine and in the case of $S$ and $O$, $S$ has a higher negative value.