The Solid State Solids have a fixed volume and shape. They vibrate but stay in relative position. When the solid is heated the atoms vibrate faster. This causes the solid to grow slightly in size. It is said to expand .
All solids expand on heating, especially metals.
Railway lines can buckle on hot days because of this expansion. If the atoms are arranged in a regular sequence, a crystal results. Metals and salts are crystaline. Glass is a good example of an amorphous solid. Metals are crystaline because their atoms are arranged in a regular sequence.