Related Clues:

• Ca++ or Cl-, e.g.
• Molecule component
• Tiny quantities
• Smithereens
• Modicum
• Tiny fraction of a joule
• Tiny power unit
• Bit of a joule
• Basic bit
• Joule fraction
• Bohr's study
• Bond component
• Element element
• It was once thought to be indivisible
• Electron's place