Atomic and Nuclear Units


Atomic Mass Unit

Neutron (n) - neutral charge =1.6749 x 10-27 kg
Proton (p) - positive charge = 1.6726 x 10-27 kg
Electron (e-) - negative charge = 0.00091 x 10-27 kg

Clearly kilogrammes are not the best unit for atomic masses

Therefore define the atomic mass unit (a.m.u or u)

1u = 1/12 mass of 12C atom = 1.66043 x 10-27 kg ~ mass of n or p

Energy Units

The unit used to measure energy at the the atomic and nuclear scale is the electronvolt (eV).
1 electronvolt = energy acquired by electron in crossing a potential difference of 1 volt

1eV = 1.60210 x 10-19 J

1 Joule = work done when a 1 newton force moves its point of application 1m in the direction of the force.