4 mistakes learners make with states of matter and the particle model, each one named and explained.
The particles are the substance. They do not melt, boil or expand; the substance does, because of how they are arranged and how they move.
The temperature stops rising and you say the heater has failed or the experiment has gone wrong.
Energy is still going in, so the temperature is expected to keep climbing.
Question. A heating graph is flat for four minutes. What is happening?
A common answer. nothing. The heating has stopped working
The answer. a change of state, with the energy going into separating the particles
Why. Energy is still arriving, but it is breaking the forces between particles rather than speeding them up.
A flat section is the busiest part of the graph, not the emptiest.
You say a puddle cannot dry up unless the water reaches 100 degrees C.
Boiling is the dramatic version of the same change, and it is the one with a number attached.
Question. A puddle dries up on a cold day. How, if the water never reached 100 degrees C?
A common answer. it cannot. Something else removed it
The answer. the fastest particles at the surface escape, which is evaporation
Why. Boiling happens throughout the liquid at one temperature; evaporation happens at the surface at any temperature.
Ask where the change is happening. Surface only means evaporation.
You draw particles with the material drawn in around them, or say there is air between the particles of a solid.
Every diagram shows circles on a page, and the page between them looks like it must be something.
Question. What is between the particles in a solid?
A common answer. the material itself, or air
The answer. nothing at all
Why. The particles are the substance. Between them in a pure solid there is nothing.
If you can name what is between them, you have added something that is not there.
You say the particles get bigger when a metal is heated, or that they melt when the solid does.
The substance plainly changes, and the particles are what the substance is made of, so they look like they must change too.
Question. A metal bar expands when heated. What happened to its atoms?
A common answer. each atom got bigger
The answer. they vibrate more and sit further apart
Why. An atom's size does not change. Expansion is extra space between atoms, not bigger atoms.
Never change the particle. Change the arrangement and the movement.
WAJD spots these patterns in your child's answers and names the one behind their wrong answers, instead of just marking them wrong.