What are the exceptions to the periodic trends in ionization energy? Why do they occur?
In general, ionization energy decreases in group and increases in period due to increase and decrease in the size respectively
However there are some exceptions due to the following factors
1) Nature of orbital or penetration power of orbitals
2) Screening effect
3) half filled and full filled orbitals
Example: In second period, the1st IE of Nitogen is greater than Oxygen due to stable half filled orbitals in nitrogen
The 1st IE of Boron is greater than Berylium due to presence of stable filled configuration and also more penetrating power of s- orbital in B
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