Why is Second Ionisation Enthalpy higher than first?

The second ionisation enthalpy is higher than the first because it requires more energy to remove an electron from a positively charged ion. When the first electron is removed, the atom becomes a positively charged ion. The remaining electrons are more strongly attracted to the nucleus, and removing another electron from this positively charged ion needs more energy.

Key Reasons

• Increased Nuclear Attraction: Fewer electrons means each one is held more tightly.
• Electron-Electron Repulsion Decreases: Less repulsion increases nuclear pull on the remaining electrons.
• Stability: The ion formed after removing one electron may be more stable, so removing another disrupts that stability.