1/2 a.m.u. 10 a.m.u. 1/1800 a.m.u. 1 a.m.u.
Electrons Neutrons Protons Neither
Electron Neutron Neither Proton
In discrete energy levels Totally randomly In random energy levels 1 circular orbit
Isotope Compound Particle Mole
Helium Lithium Beryllium Hydrogen