how many electrons does a fluorine atom have in its second shell?
Oxygen has 8 electrons --- 2 in the first shell, and 6 in the second shell (so six valence electrons). Fluorine has 9 electrons --- 2 in the first shell, and 7 in the second shell (so seven valence electrons). Neon has 10 electrons --- 2 in the first shell, and 8 in the second shell (so eight valence electrons).