HPQ:[Chemistry]:[KS3]:[materials]:[L Doyle]

Solids expand when heated because:
 
A. The particles move more quickly
B. The particles get bigger
C. The spaces between the particles get bigger
D. The heat gets trapped between the particles 
 
Answer: C
 
 
 

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Karen Hornby

When a solid is heated, the atoms of the solid do gain kinetic energy and begin to vibrate more vigorously. Because the atoms are vibrating more, or moving more around a fixed point, they occupy slightly more space and as a result the solid expands in all directions. A bit like when you wave your hand - it takes up more space because it is moving, not because the hand has expanded.

You may find this model useful for demonstrating this to students:

http://www.nuffieldfoundation.org/practical-physics/model-vibrating-atoms-solid

There are also some other great resources/activities for particle theory in this resource package: http://www.nationalstemcentre.org.uk/elibrary/list/9249/states-of-matter-and-particle-theory

There are lots more resource packages for the KS3 curriculum here: http://www.nationalstemcentre.org.uk/secondaryscience