If atoms are individual LEGO bricks, then molecules are the structures you build by snapping those bricks together. A molecule forms when two or more atoms join through chemical bonds, creating something entirely new. Take water — the most famous molecule on Earth. Two hydrogen atoms bond with one oxygen atom to form H₂O. Separately, hydrogen is a flammable gas and oxygen feeds fires, but together they create the liquid that sustains all life. That is the magic of molecules: the whole is dramatically different from the parts.
Molecules range from beautifully simple to mind-bogglingly complex. The oxygen you breathe right now is O₂ — just two oxygen atoms linked together. Table sugar (sucrose) is C₁₂H₂₂O₁₁, a cluster of 45 atoms. And DNA, the molecule carrying your genetic blueprint, contains billions of atoms arranged in a famous double-helix spiral. Every scent you smell is a molecule floating through the air and docking into receptors in your nose. Every flavor you taste is a molecule interacting with your tongue.
It is important to note that not all substances are made of molecules. Table salt (NaCl) is actually an ionic compound — a vast lattice of sodium and chloride ions, not discrete molecules. Similarly, metals like iron or gold consist of atoms bonded in massive metallic networks. The term "molecule" specifically describes a distinct, countable group of covalently bonded atoms. So while every molecule contains atoms, not every group of atoms is a molecule.