Would you expect the second electron to gain enthalpy of oxygen as positive, more negative or less negative than the first one? Give reason.

The enthalpy change associated with adding electrons to an atom is known as electron affinity. When considering oxygen, the first electron added to a neutral oxygen atom typically has a more negative enthalpy change compared to the second electron.

Understanding Electron Affinity

The first electron affinity of oxygen is quite exothermic, meaning it releases energy when the electron is added. This is because the added electron experiences a strong attraction to the positively charged nucleus.

Behavior of the Second Electron

However, when a second electron is added to the already negatively charged oxide ion (O⁻), the situation changes. The second electron experiences repulsion from the first electron due to their like charges. This repulsion makes the process less favorable.

• First Electron: Strong attraction to the nucleus, more negative enthalpy.
• Second Electron: Increased repulsion, less negative enthalpy.

As a result, the enthalpy change for the second electron is less negative than that of the first. In summary, you would expect the second electron's enthalpy to be less negative due to the repulsive forces at play.