(Lower Sec Science) Do atoms expand when heated?

We learned from primary science about the general properties of matter such as that matter expands when heated. In lower secondary, we learned to use the particulate model or theory to explain the general properties of matter. In other words, we are starting to zoom into the microscopic world of particles to help to explain the macroscopic aspect of matter. In the particulate theory of matter, spheres or solid balls are used to represent particles.

When asked to explain why matter expands when heated, some students thought that particles expand when heated. This is a common misconception. Particles (such as atoms and molecules) don't become bigger or smaller. But they do move faster or slower.

Particles don't expand and contract... 

Here is the correct explanation. When heat is supplied to matter, the kinetic energy of particles increases. The particles collide with one another with greater frequency and greater speed (and therefore with greater force). The particles become further apart (or the separation between particles increases) and so matter expands.

Particles move faster or slower...