The atomic mass of fluorine is 18.998 amu and its mass spectrum shows a large peak at this mass. The atomic mass of chlorine is 35.45 amu, yet the mass spectrum of chlorine does not show a peak at this mass. Explain the difference.

I saw this question on here, but I didn't really understand the one answer someone sent in nor the concept.

Question

The atomic mass of fluorine is 18.998 amu and its mass spectrum shows a large peak at this mass. The atomic mass of chlorine is 35.45 amu, yet the mass spectrum of chlorine does not show a peak at this mass. Explain the difference.

I saw this question on here, but I didn't really understand the one answer someone sent in nor the concept.

aaronq · Answer

Is it about isotopes? i'm not really sure. What was the answer you saw?