Science > Chemistry > States of Matter > Introducion
A matter is defined as anything that has mass, which occupies space and may be perceived by senses. There are three states of matter, viz. (a) solid, (b) liquid, and (c) gaseous states. Whatever may be the state of matter, it is composed of particles. In this article, we shall study the particle model of matter.
Particle and Kinetic Model of Matter:
The particle model is also known as a dynamic particle model. On the basis of the particle model, different states of matter can be explained easily. Some assumptions of this model are as follows.
- All matter is made of tiny particles. However, the arrangement and the distribution of particles are different in the three states of matter.
- Empty spaces exist between these particles. These empty spaces are called voids.
- The particles exert force attraction on one another but the magnitude of these interparticle forces is different in the three states of matter.
- The particles are not stationary and have a tendency to acquire motion. In solids, they are fixed at a position and only vibrate about their mean position. In liquids and solids besides vibrational motion, the particles have translatory motion.
- With the increase in the temperature the kinetic energy of the particles hence the thermal energy increases.
Evidence of Particle Nature of Matter:
If we add potassium permanganate in water kept in a glass jar. We can observe the purple coloured particles separate from the crystals of potassium permanganate and spread in water. Ultimately whole water turns purple.
If we add crystals of salt in water, they settle at the bottom. Gradually their size starts reducing and ultimately the crystal disappear but whole water gets a uniform salty taste. Besides the volume of water does not increase. it indicates salt particles occupy inter-particulate spaces.
When a scent bottle is opened at one corner of a room the fragrance can be smelt at any corner of the room. The molecules of scent occupy the inter-particulate space.
Evidence of Kinetic Nature of the Particles of Matter:
The English Botanist Robert Brown, in 1927 observed that colloidal particles exhibit continuous random motion in all directions in a straight line. He found such movement when pollen grains were suspended in water.
The phenomenon of continuous zig-zag movement of colloidal particles in straight-line paths in a random direction is known as a Brownian movement. A pollen grain is placed on the surface of water taken in a beaker. It shows the Brownian movement. The pollen grain is surrounded by a large number of water molecules that constantly bombard the pollen grain. On unequal bombardment, the pollen grain gets pushed in certain directions. This experiment proves the kinetic nature of particles of matter.
Characteristics of Particles of the matter:
Particles of matter are very small.
All matter is made up of very small particles that are not visible to naked eye. It can be proved by the following experiment. Take two or three crystals of potassium permanganate and add them in 100ml of water. The solution formed is deep purple in colour. Now take 10ml of this solution and add it to another beaker containing 00ml of fresh water, again you will observe that the colour of the water will change but the solution will be faint compared to that in the first case. Repeat this procedure four or more time. In every step, we observe that the colour of the water changes but it will become fainter and fainter.
The solution remains coloured even at a very high dilution. Which shows that potassium permanganate added is broken into very very small particles exhibiting their characteristic properties. Hence we can conclude that particles of matter are very very small.
Particles have spaces between them.
If we add crystals of salt in water, they settle at the bottom. Gradually their size starts reducing and ultimately the crystal disappear but whole water gets a uniform salty taste. Besides the volume of water does not increase. it indicates salt particles occupy inter-particle spaces present between water particles.
Particles are constantly moving.
A pollen grain is placed on the surface of water taken in a beaker. It shows Brownian movement. The pollen grain is surrounded by a large number of water molecules which constantly bombard the pollen grain. On unequal bombardment, the pollen grain gets pushed in certain directions. This experiment shows that the particles of matter are constantly moving. Thus they possess kinetic energy. As the temperature rises, particles move faster. Hence with the increase in temperature the kinetic energy of the particles also increase.
Particles Attract each other.
Particles of matter have a force acting on them. This force keeps the particles together. The strength of this force of attraction varies from one kind of matter to another. This force of attraction varies from substance to substance it can be verified by the fact that some forces can be powdered by applying small force, while some break into crystals, while some do not break. This force of attraction between the particles of the same substance is called cohesion. The attractive forces between the particles are maximum in solids and minimum or negligible in case of gases.
States of Matter on the Basis of Particle and Kinetic Model:
Solid State:
At room temperature, the particles of solids occupy definite positions. They can vibrate about their mean positions, but they cannot move from one position to another. The particles are bound to one another strongly. Hence solids have definite shape and definite volume.
Liquid State:
The particles of liquid do not have fixed positions, and they slide over one another within the bulk of the liquid. Thus particles can move from one position to another, but cannot leave the bulk. The particles are bound loosely. Hence liquids have definite volume but don’t have a definite shape. They take shape of the container in which they are kept.
Gaseous State:
In gases, the particles lie far apart and exert a very weak force of attraction on one another. Actually, the particles of gas are in random motion can change position continuously, and can move away from each other. They occupy the whole space available. Only walls of containers restrict their movement. Hence gases have neither definite shape nor definite volume.