Why do potassium, rubidium, cesium all have lower standard potentials than sodium? Why do potassium, rubidium, cesium all have lower standard potentials than sodium?


Sodium has a higher charge density than any of them, so its enthalpy of hydration should be larger, right? The argument applies for why lithium has a more negative standard reduction potential than the other three, but why doesn't this argument apply for sodium?
I think lithium is the outlier in this series due to the enthalpy of hydration. The trend from sodium to caesium is linear and consistent with ionization energies, meaning the enthalpies of hydration are not big enough to account for the difference in ionization entropies, thus the trend.