<p><strong>Fig. 2.21.</strong>&nbsp; (<strong>A</strong>) Hydrogen atom (atomic number 1, 1 proton, 1 electron) (<strong>B</strong>) Oxygen atom (atomic number 8, 8 protons, 8 electrons). Note that not all of the protons and neutrons are visible. (<strong>C</strong>) Sodium atom (atomic number 11, 11 protons, 11 electrons) Note that not all of the protons and neutrons are visible.</p>

Fig. 2.21.  (A) Hydrogen atom (atomic number 1, 1 proton, 1 electron) (B) Oxygen atom (atomic number 8, 8 protons, 8 electrons). Note that not all of the protons and neutrons are visible. (C) Sodium atom (atomic number 11, 11 protons, 11 electrons) Note that not all of the protons and neutrons are visible.

Image by Byron Inouye