I know that in general, the first ionization energy increases across a period due to increasing nuclear charge, reasonably constant shielding & decreasing atomic radius.
From N to O, however, the I.E anomalously decreases. The reason usually given is that the spin pair repulsion between the 2px2 electrons in oxygen outweigh the effect of the increased nuclear charge.
However, the additional electrons in F & Ne are also spin-paired. Why doesn't the extra spin pair repulsion outweigh the extra nuclear charge in this case? http://www.chemguide.co.uk/atoms/properties/ies.html#top says
Between nitrogen and oxygen, the pairing up is a new factor, and the repulsion outweighs the effect of the extra proton. But between oxygen and fluorine the pairing up isn't a new factor, and the only difference in this case is the extra proton. So relative to oxygen, the ionisation energy of fluorine is greater. And, similarly, the ionisation energy of neon is greater still.
But I don't understand how being a new factor or not makes any difference on its effect. It's not like the atom adapts to the new factor in O, reducing its effect its effect in F & Ne