the highest occupied energy level of elements is filled and stable

Question

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Answer 1

The highest occupied energy level is known as the valence shell.  If the valence shell is fully occupied, the element is stable and unreactive.  The elements in the periodic table that have a full valence shell are Group 18, the noble gases, listed below along with the electron configuration of their valence shell:

 

He = 1s2
Ne =[He]+2s22p6
Ar = [Ne]+3s23p6
Kr = [Ar]+4s23d104p6
Xe =[Kr]+5s24d105p6
Rn =[Xe]+6s24f145d106p6

The general configuration is that their valence electron orbitals are completely filled with electrons.