Ionization Enthalpy ($$\Delta_i H$$ ) Exceptions

Anomalous Orders:

$$\text{IE}_1(\text{Be}) > \text{IE}_1(\text{B}) \qquad \text{and} \qquad \text{IE}_1(\text{N}) > \text{IE}_1(\text{O}) \qquad \text{and} \qquad \text{IE}_1 < \text{IE}_2 < \text{IE}_3$$

Concept: Orbital penetration effects make removing electrons from fully-filled $$ns^2$$ shells ($$\text{Be}$$) harder than $$np^1$$ configurations ($$\text{B}$$), while exchange energy gives extraordinary stability to half-filled $$np^3$$ shells ($$\text{N}$$) over $$np^4$$ states ($$\text{O}$$).

Notation:

• $$\text{IE}_1, \text{IE}_2, \text{IE}_3$$ = Successive ionization states; Large step-wise spikes indicate breaking into stable noble gas cores.