In the context of the Bridge Electromagnetic Theory, a quantum-relativistic theory based on Maxwellian electromagnetism, it has recently been shown that the characteristics of a hydrogen atom can be obtained through an electron-proton orbital capture process forming a non-radial emitting dipolar electromagnetic source. The model structurally different to the Bohr-Sommerfeld and Schrödinger models has now been deepened and completed by testing it on the properties of hydrogen and deuterium atoms and of helium and lithium in hydrogenoid form. These last two atoms are of cosmological interest as they are the heaviest elements produced by electron capture in the early universe. The theoretical results obtained regarding the atomic structure and spectra are in excellent agreement with the observational data and suggest that the electron-nucleus interaction is influenced on an isotopic basis as a function of the inertial mass value of the nuclei.