Radiometric dating requires that the decay rates of the isotopes involved be accurately known, and that there is confidence that these decay rates are constant. The physical constants (nucleon masses, fine structure constant) involved in radioactive decay are well characterized, and the processes are well understood.Careful astronomical observations show that the constants have not changed significantly in billions of years—spectral lines from distant galaxies would have shifted perceptibly if these constants had changed.
"Atomic decays" are due to proton or neutron decays: either weakly, incrementing up or down the table of elements; or strongly, often splitting into smaller elements, one of which is often helium.
That is, electrons can move closer to or farther away from the nucleus depending on the chemical bonds.
This affects the coulomb barrier involved in Alpha decay, and therefore changes the height and width of the barrier through which the alpha particle must tunnel.
Any incoming negative charge would be deflected by the electron shell and any positive charge that penetrated the electron shells would be deflected by the positive charge of the nucleus itself. "Decay" simply refers to a meson or baryon becoming another type of particle, as the number of a certain type of particle goes down or decays as they are converted.
This can happen due to one of three forces or "interactions": strong, electromagnetic, and weak, in order of decreasing strength.
The effect of this on alpha decay, which is the most common decay mode in radiometric dating, is utterly insignificant.