Possible Clues:

• Atoms with + or - symbols
• Table salt is made of them
• Chem 101 study
• Particles with pluses or minuses
• Sci-fi beam makeup
• Atoms that have lost electrons, for instance
• Atoms that have an unequal number of protons and electrons
• Atoms that may be radical
• Plural suffix with "bill"
• Positive particles, perhaps