Related Clues:

• Physicist's study
• 'Am ___ time?'
• 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