Related Clues:

• Minute amount
• + or - item
• Molecule part
• Item of interest to Niels Bohr
• Negatively charged particle
• Itty-bitty bit
• First half of the files?
• It may have an extra electron
• Physics subject
• See 41-Down
• Smashed item
• Hydrolysis atom
• Tiny part
• Ca++ or Cl-, e.g.
• Molecule component