Given the shell model of the atom, suggest a possible reason that Lewis proposed a maximum of two electrons for hydrogen and a maximum of eight electrons for carbon, nitrogen, oxygen, and fluorine.

2 answers

Two electrons fit in the first shell out from the nucleus and eight fit in the second. Every element with more protons than the two of Helium needs to work on shells outside the first one. one you get to ten, you have filled the first two shells.
I found this on the Internet as to WHY Lewis suggested just 2 electrons for H; i.e., why not 8 for it as well as for other elements.
In a water molecule, oxygen forms one covalent bond with EACH of TWO hydrogen atoms. As a result, the oxygen atom has a stable arrangement of 8 valence electrons. Each hydrogen atom forms only one bond because it needs only two electrons to be stable.

Note: the caps are my additions to the copied material.