PPT
Atomic Number. Number of Protons. Always an integer!. Mass Number. Number of Protons + Neutrons. Always an integer!. 12 C. Left Superscript = mass number. 6. 12 C. Left Subscript = atomic number. 6. 80 Br. 35. 35. Atomic Number = ?. 20 Ne. 10. 20. Mass Number = ?. 27 Al. 13.