Question

By a common principle used in mass spectrometry, what element is most likely to be present in a molecule which has a molecular ion mass of 227?

a.		oxygen
b.		chlorine
c.		sulfur
d.		nitrogen

Please explain why

Answer 1

According to a principle in Mass Spectrometry (The Nitrogen Ring rule), if a molecule has odd number of nitrogens, the molecular ion will have an odd number and if the molecule has even number of nitrogens, the molecular ion will have even number.

Because the given question says that the molecular ion mass of 227, which is an odd number, it means that the molecule contains odd number of nitrogens in it.

Most elements in neutral states form even number of bonds when their masses are in even number and odd number of bonds when their nominal masses are even numbered.

But this is not the case when nitrogen is present. Because it has a nominal mass of 14 (even numbered) but its valency is 3. Therefore can form only three bonds!