Comment upon the following:

Rigidity, Compressibility, Fluidity, Filling a gas container, Shape, Kinetic energy and Density.

(i) Rigidity- Property of the Substance to retain/maintain their shape when subjected to outside force is known as Rigidity. This property is determined by the inter molecular force of attraction.Solids are the most rigid because of its strong force of attraction followed by liquids and then gases.


(ii) Compressibility. The particles of matter have intermolecular spaces. If an external force is applied, it can bring these particles closer. The property of a fluid or a solid due to which its volume decreases when pressure is applied is called Compressibility. The particles in gas have large spaces between them. When the pressure is applied on a gas its volume decreases to large extent. Hence, gases have high compressibility. On the other hand, the particles in solids and liquids are closely packed, so solids and liquids do not have much compressibility.

(iii) Fluidity. The tendency of the particles to flow is called Fluidity. Gases and liquids exhibit the property of fluidity, so they are called fluids.This property is determined by intermolecular force of attraction as well as intermolecular spaces Due to large intermolecular spaces and very weak forces of attraction, gases can flow very easily followed by liquids and then solids which have almost negligible fluidity.

(iv) Filling a gas container. A gas is able to fill the container because its particles are able to vibrate randomly in all the directions. The particles of gas have very high kinetic energy and very negligible forces of attraction. As a result, gases are able to fill the container fully.

(v) Shape. The external form or appearance of a substance is called its Shape. The particles in a solid have very strong forces of attraction due to which they are closely packed and occupy fixed positions. As a result, solids have fixed shape. The liquids and gases have comparatively weaker forces of attraction between them as a result they take the shape of container in which they are stored.

(vi) Kinetic energy. The energy possessed by particles due to their motion is called kinetic energy. At a given temperature, the particles of a gas have the maximum kinetic energy. This is because the force of attraction among the particles is very weak. Liquids have lesser kinetic energy as compared to whereas solids have the least kinetic energy at a given temperature.

(vii) Density. The mass per unit volume of a material is called its density. Solids have high densities. This is because their particles have very strong forces of attraction and are packed very closely. Liquids have usually lower densities than solids because their particles are loosely packed as compared to solids. Gases have the lowest densities because their particles are very far away from one another due to weakest forces of attraction among them.