# Variation in atomic sizes in the transition elements

From left to right across a period, effective nuclear charge increases in the transition series, just like in the p block, and so atomic size decreases. Here the electrons are being added to the d orbital, where shielding is relatively poor compared to the p orbital. It should follow that the increase in the effective nuclear charge is more significant for the transition elements than the p block in a given period, leading to greater size variation among successive members - but the size variation is smaller in the transition elements instead. In fact atomic size increases from Ni to Zn. Is there any logical explanation for the fact?

From Ni to Zn, Z$_{eff}$ decreases and the shielding effect increases . Z$_{eff}$ is inversely proportional to the size, so if Z$_{eff}$ decreases, size will increase. That's why there is some uncertainty in the order of size for 3d series.