# I Mass different for neutrons?

1. Jun 6, 2017

### Chenghui Yuan

My physics is not good, please kindly don't judge my physics.
In some molecular weight calculator to get mono-isotope neutral mass for atoms listed below.
In FTICR, we could find these difference. For example,
m/z 101.960035, ^1H^35Cl^16O3^18O
m/z 101.952838, ^1H^37Cl^16O4
Here is my question. Do neutrons have different mass and why or good explanations?
Thanks.

16^O 15.994915
18^O 17.999161
difference 2.004246
35^Cl 34.968853
37^Cl 36.965903
difference 1.99705

2. Jun 6, 2017

### Staff: Mentor

All neutrons have the same mass, as do all protons. However, if you take two or more of these particles and bring them together in an atomic nucleus, some energy will be released and because of Einstein's $E=mc^2$ the mass of the nucleus will be less than the mass of the individual nucleons (neutrons and protons) of which the nucleus is composed.

If you google for "binding energy" you will find a bunch of more detailed explanations and examples.

Last edited: Jun 7, 2017
3. Jun 7, 2017

### Chenghui Yuan

Thanks a lot. This is what I search for.