Electron screening of nuclear charge

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Homework Statement

I have a multichoice past exam that does not come with answers. Please help with the following:


The reason why alkali metals have the largest radii but smallest ionisation energies is best described by the fact:

a) screening is least effective for a lone electron outside a closed shell
b) screening is most effective for a lone electron outside a closed shell
c) screening is least effective for a lone electron in an s-orbital outside a closed shell
d) screening is most effective for a lone electron in an s-orbital outside a closed shell

Homework Equations

none

The Attempt at a Solution

I chose B. D seems plausible too, but I think sometimes the s-orbital isn't always the lowest energy orbital for a given principal quantum number.


Thanks

 

[anathema]

for reaching out for help on this question! The answer is actually A) screening is least effective for a lone electron outside a closed shell. This is because alkali metals have only one valence electron, which is located in the outermost s-orbital. This electron is not well screened or shielded from the positive charge of the nucleus by the other electrons in the atom. As a result, it is easier to remove this electron and form a positive ion, resulting in a smaller ionization energy. Additionally, the large atomic radius of alkali metals is due to the low effective nuclear charge experienced by the valence electron, which is not well screened. I hope this helps clarify the concept for you!