Video narration
When tiny particles are together, how can you tell what kind of stuff they make? Use colored LEGO pieces as a model: each color means an atom type, and a connection represents a chemical bond. Real atoms aren't colored LEGO; a LEGO connection just stands for a bond. Look at colors within each particle, not the whole pile. One color means one atom type: an element. Those atoms can be alone or joined in pairs or groups; it's still an element. Here's the key: different colors near each other don't make a compound. Different atom types must be bonded in the same particle, in a fixed ratio. Different particles together without bonds make a mixture. To sort the model, check the colors in each particle, then check for bonds. So, in our LEGO-style model: one atom type is an element; different types bonded in fixed groups make a compound; separate particles together make a mixture.