Question

The electronic configuration of potassium is 2,8,81.Why does the last electron of potassium go to fourth shell instead of occupying the third shell,even though the third shell has the capacity to accommodate ten more electrons?

Answer 1

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The electronic configuration of potassium is 2,8,8,1 and not 2,8,9 because an atom can have only 8 electrons in its valence or last shell. If the electronic configuration was 2,8,9 then the valence shell would exceed its maximum capacity that is 8. This actually happens  because the k,l,m,n.... shells are again divided into some orbitals s,p,d,f.... . This orbitals have a capacity according to which the electrons in k,l,m,n... shells are present.