Atoms Keep Score

everything on the right got there from the left. there is nowhere else.

pull atoms off their bonds and across the arrow — the count has to come out even

Nothing here balances because a rule says so: exactly the atoms on the left fit the sockets on the right, and your finger is the only way one crosses. A dropped atom springs back to its bond -- conservation of mass.

Concepts: chemistry, conservation.

An interactive you play with one thumb, on Wundr.