Question

Why are solids hard? Why is the volume of solid is definite?

Answer 1

Hint:Any substance occupying space and has a mass can be termed as matter. Matter is broadly distinguished into three major forms on the basis of the differences in their bulk properties, namely solids, liquids and gases.

Complete answer:
Solids can be characterized by a definite volume and shape. Liquids can be characterized by their ability to adapt to the shape of the container they are kept in and gases can be characterized by their ability to adapt to the shape as well as the volume of the container they are stored in.
The molecules of gases and liquids are present far apart from each other. In other words, they have more gaps or intermolecular spaces. Due to the large intermolecular forces, the intermolecular attractions are very less and thus liquids and gases can flow. Thus, they do not have a definite volume (liquids have a definite volume) and shape. On the other hand, solids have very less intermolecular spaces. The intermolecular forces are high giving them a definite shape and making them rigid.

Thus, solids are hard and have definite volume.

Note:
Solids are rigid and hard with a definite shape and volume. However, amorphous solids have a tendency to flow at a very slow rate. They are commonly known as pseudo solids or super cooled liquids due to this property. A common example is a glass panel fixed to a window or door of a very old building. If they are observed carefully, we will find that the glass is slightly thicker at the bottom than that at the top. The reason for this is that glass is an amorphous solid and flows very slowly under the influence of gravity making the lower portion of the panel thicker than the upper.