Why is the Ionisation enthalpy of hydrogen higher than that of sodium?
We know, the size of H atom is much smaller than that of Na atom. Due to which electrons are situated at a distance in Na from the nucleus as compared to that of H atom. As a result nuclear attraction received by the valence electrons is much higher for H atom than Na atom. So, there would be difficulty in removing a valence electron from H atom than Na atom due to higher nuclear attraction, so more energy would be required. Thus, ionisation enthalpy of hydrogen is higher than sodium.
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Justify the position of hydrogen in the periodic table on the basis of its electronic configuration.NCERT - Chemistry Part-II