An atomic note contains exactly one idea.

Not one topic. Not one article. One claim that can stand on its own.

Bad: "Notes on WWII" (a topic, not a thought) Good: "The Molotov-Ribbentrop pact delayed Germany's eastern front by 2 years" (a claim)

Atomic notes are easier to link because they have a clear identity. You know when two notes belong together.

Related: zettelkasten, @carol / on-music-theory-as-a-language