Why can you smell lunch from the hallway , but you can't smell a rock?
Everything around you , your phone, the air you breathe, the water in your bottle , is made of particles too small to see. The particle model is the framework chemists use to explain why different materials behave so differently, all by thinking about what those invisible particles are doing.
The model rests on four ideas your exam will expect you to know cold. First, every substance is built from tiny particles , these might be atoms, molecules, or ions depending on the substance. Second, those particles are never sitting still; they're always moving, and the hotter things get, the faster they go. Third, particles attract each other , sometimes strongly, sometimes barely at all. Fourth, there's space between particles, and how much space there is controls properties like density and whether you can squash something.
Particle model: A framework that explains the behaviour of matter by describing the arrangement, movement, and interactions of the tiny particles that make up every substance.
The surprising moment: your intuition says a solid must have stronger particle attractions than a liquid, because solids hold their shape. Usually true , but ice breaks this rule. In solid ice, water molecules lock into an open, spread-out lattice held by up to four hydrogen bonds each. In liquid water, those bonds keep snapping and reforming, letting molecules pack slightly closer together on average. The result? Liquid water is actually denser than ice , which is why ice cubes float instead of sinking to the bottom of your drink.
The particle model is a simplification , real particles don't behave perfectly. But for MYP level, it explains almost everything the exam will throw at you.
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