## Chemistry: The Science in Context (4th Edition)

(a) To figure out how many electrons a neutral atom of fluorine (F) contains, we look to the periodic table. Fluorine has an atomic number of 9, so there are 9 protons. In a neutral atom, the number of protons equals the number of electrons; therefore, this atom of fluorine also contains 9 electrons. (b) An oxygen atom is atomic number 8, which means it has 8 protons. In a neutral atom, oxygen should have 8 electrons. However, in this situation, oxygen has a 2- charge, meaning it has two extra negative charges or two extra electrons. Therefore, this O$^{2-}$ has 10 electrons instead of the regular 8. (c) A sulfur atom is atomic number 16, which means it has 16 protons. In a neutral atom, sulfur should have 16 electrons. However, in this situation, sulfur has a 2- charge, meaning it has two extra negative charges or two extra electrons. Therefore, this S$^{2-}$ has 18 electrons instead of the regular 16. (d) A chlorine atom is atomic number 17, which means it has 17 protons. In a neutral atom, chlorine should also have 17 electrons. Therefore, this neutral atom of chlorine has 17 electrons. Option (c) is correct because S$^{2-}$ has 18 electrons, the most of any of the other options.