Historical clue formulations

• Something that's free of charge — 2017-12-17
• Deuterium has one — 2011-09-30
• *Particle with no electric charge — 2009-10-19
• Discovery of Sir James Chadwick — 2003-10-11
• Atomic particle — 1998-12-30
• "_____ Dance" (Pointer Sisters hit) — 1994-11-13