# Do low atomic numbers not obey Moseley's law?

mukul
Helium has k-alpha of 24.5 eV whereas if we derive it using Moseley's law, then it is supposed to be 10.2 eV

Also I then looked into many sources and found that Moseley's graph talks about elements having z>=10 only

Later I found in few sources that the assumption that "one electron shields the nucleus and thus we should replace Z by Z-1 in Rydberg formula" is not entirely correct
$$E=13.6(Z-1)^2(\frac{1}{1^2}-\frac{1}{2^2})$$
as the effect due to shielding is little less than expected and should be taken into account.
source: https://www.physicsforums.com/threa...ion-energy-than-hydrogen.454607/#post-3028358

My question is why is this effect (that K-shell electron's shielding effect is less than 1) not applicable as we move up in the periodic table i.e. for z>=10