# Why are higher oxides of non-metals more acidic?

I have studied that if the electronegativity difference between O- and element M is more then it is a basic oxide and if the difference is less then it is an acidic oxide. However, it is a fact that higher oxides of Non metals are more acidic than lower oxides. If the theory concerns polarisation, is it not contradictory?

• Getting idea about cutting out "acidic oxides" out of every textbook and forcible teaching the authors the Lux-Flood theory, after seeing this... Mar 26 '19 at 23:14

It is expected oxides with more polar $$\ce{M-O}$$ bonds are stronger Lewis bases than those with less polar bonds.
Furthermore, for the same element, the polarization gets weaker/Lewis alkality weaker when more $$\ce{O}$$ atoms are attached.
It is well observable that acids like $$\ce{HNO3}$$, $$\ce{HClO3}$$, $$\ce{HClO4}$$, $$\ce{H2SO4}$$, $$\ce{HBF4}$$ are strong, as the delocalization has a good sandbox to play in.