Answer
F-19 has a very large percent abundance which explains why the atomic mass of fluorine is nearly 19.00 amu. Cl-35 and Cl-37 both have significant percent abundances, therefore, its atomic mass is the weighted average, which occurs somewhere in between these two masses. Therefore, the mass spectrum does not peak here.
Work Step by Step
F-19 has a very large percent abundance which explains why the atomic mass of fluorine is nearly 19.00 amu. Cl-35 and Cl-37 both have significant percent abundances, therefore, its atomic mass is the weighted average, which occurs somewhere in between these two masses. Therefore, the mass spectrum does not peak here.
