Passage: The type of atom is determined by the atomic number (i. e. the number of protons). The atomic mass of an atom is approximately the number of protons plus the number of neutrons. Typically, the atomic mass listed in a periodic table is an average, weighted by the natural abundances of different isotopes. Answer: atomic number
Adding the number of protons plus the number of neutrons in an atom, decides it's approximate mass, what is another word for this value?