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- 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.
Historical Perspective of States of Matter:
- Ancient Indian philosopher suggested that all the forms of matter are made up of five basic elements (they called it tatva) they called these five basic elements as ‘panch maha bhoota’. These elements are the sky (Akash), air (vayu), fire (teja), water (aap) and earth (soil).
- Ancient Greek philosophers considered that all for of matter are made of fire, water, air and the earth.
- Thales (640-546 BC) suggested that all things arose from the water.
Different States of Matter:
- It has a definite shape and definite volume at given temperature and pressure. A substance is said to be in the solid state if its melting point is above the room temperature at the atmospheric pressure. e.g. Chair, chalk, desk, salt, silver etc.
Characteristics of Solid State:
- Solids have a definite shape and volume.
- There are strong cohesive forces between the molecules of solid.
- The molecules of solid are fixed at one point.
- The melting point of the solid is above the room temperature at the atmospheric pressure.
- Solids have high densities.
- e.g. iron block
- It has a definite volume but has indefinite shape. It will take the shape of the container containing it.A substance is said to be in the liquid state if its boiling point is above the room temperature and melting point is above the room temperature at the atmospheric pressure. e.g. water, alcohol, milk etc.
Characteristics of Liquid State:
- Liquids do not have a definite shape but have a definite volume
- In liquids, the cohesive forces are weaker compared to solid and stronger compared to gases.
- Molecules of liquid move freely anywhere but can’t leave the bulk.
- The boiling point of a liquid is above and its freezing point (melting point) is below the room temperature at the atmospheric pressure.
- Liquids have comparatively low densities compared to solids but have higher densities than the gases. e.g. water
- Gas has neither a definite shape nor a definite volume. It takes shape and volume of the container. Thus it occupies whole available volume. A substance is said to be in the gaseous state if its boiling point is below the room temperature at the atmospheric pressure. e.g. air, oxygen, nitrogen, carbon dioxide.
Characteristics of Gaseous State:
- Gases have neither definite shape nor a definite volume.
- In gases, the intermolecular forces of attraction are very weak i.e. almost zero.
- Molecules of gases move freely anywhere.
- Condensation point (boiling point) of gas is below the room temperature at the atmospheric pressure.
- Gases have very low densities. e.g. hydrogen.
Note: By changing the temperature or pressure or both, the state of the substance can be changed.
- Note: Besides these three standard states of matter, there are two more states called plasma state (Exists at very high temperature) and Bose-Einstein condensate (Exists at very very cold condition).
- This state exists at superheated gaseous state consisting of a mixture of electrons and positively charged ions with unusual properties. These particles are super energetic and are at super excited state.
- It is found at extremely high temperatures such as interiors of suns and stars or intense electric fields as a discharge tube. Astronomers reveal that 99% of all matter in the universe exists in the plasma state.
Bose-Einstein Condensate (1924):
- This state was predicted by Einstein and proved by Satyendra Nath Bose in 1920. It is supercooled solid in which atoms lose their separate identity. They get condensed and behave like a single super atom.
- This state is very useful for the modern concept of superconductivity.
Particle Model and Kinetic Model of Matter:
- Particle model is also known as dynamic particle model. 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.
- On the basis of particle model different states of amtter can be explaines easily.
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.
- These observations prove the particle nature of matter.
Evidence of Kinetic Nature of the Particles of Matter:
- Brownian movement:
- 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 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 proves 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.
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