The light elements use a Lewis octet rule for electrons in molecules.   
   I have discovered that the 8 is from the cube at the core of the nucleus.   
      
   8 = 2 + 6   
      
   6 is the number of faces on a cube   
      
   2 is the number of protons in the core cube of 2x2x2   
   protons and neutrons.   
      
      
   http://pyramidalcube.blogspot.com/2017/08/periodic-table-of-shap   
   s-of-nuclei.html   
      
   Also the 32 electron rule for Lanthanides also has the same reason:   
      
      
   32 = 14 + 18   
      
      
   14 is number of protons in cube   
      
      
   18 = 6*3   
      
   6 faces on a cube   
      
   3 protons on the tip of protons on each face   
      
   More details are available. In summary, 8 is the sum of   
   salient protons in a nucleus: cube protons and tip   
   protons on the nucleus.   
      
   Alan Folmsbee   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)