The best replacement for ions is isotopes.

The best alternatives to ions are rated as following:
★★★★★  isotopes
★★★★★  atoms
★★★★  molecules
★★  ozone
★★  positive ions
★  negative ions
★  radicals
★  free radicals
★  anions
★  eons
★  compounds
★  cations
★  electrons
★  two atoms
  atoms bigger
  groups of atoms
  hydroxide ions
  silver nanoparticles
  binary compounds

Your alternative for ions is not listed? Suggest!
Speaking about ions, one probably shouldn't forget about same electron configuration.

Other search terms related to ions and their ratings are:
★★★★★ same electron configuration
★★★★★ variable oxidation numbers
★★★ noble gas configuration
You have in mind a companion for ions and it is not yet here? Propose!



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ions
isotopes
atoms