Ionization Energy Within a Period

In a period, since the atomic radius decreases from left to right, the ionization energy generally increases. 

In group B elements (transition and inner transition metals), there are no fixed jumps between the two consecutive ionization energies. That is why we cannot talk about the relationships of ionization energies of these elements. 

Which atom of the 3Li and igK would have the higher first ionization energy  

Let us first write the electron configurations of these atoms. 

From the electron configurations we can see that lithium is in the 2nd period, group 1A, and potassium is in the 4th period, group 1A. Since lithium is above potassium in the same group, the atomic radius of lithium is smaller than that of potassium but the first ionization energy is higher. 

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