In our daily life, we come across many objects, the knowledge about which can be gained by one or more of our senses like sight, touch, hearing, taste and smelling. These objects possess mass, occupy space and may have different shapes, sizes and colours. All these objects constitute matter. Matter may thus, be defined as anything that occupies space, possesses mass, offers resistance and can be felt by one or more of our senses. Some examples of matter are, water, air, metals, plants, animals, etc. Thus, matter has countless forms. The matter can be classified into different categories depending upon its physical or chemical nature. Matter is categorized as a gas, a liquid or a solid on the basis of physical state. Air is gas, water is liquid whereas sand is solid. Gases and liquids are fluids but solids are rigid.
On the basis of chemical nature matter is classified as an element, compound or mixture.
Elements and compounds are pure substances whereas mixtures contain two or more pure substances.
In this Unit, we shall study classification of matter on the basis of its physical properties.
PARTICULATE NATURE OF MATTER
- Matter is made up of small particles
The particle nature of matter can be demonstrated in activity 4.1:
ACTIVITY4.1
To demonstrate particle nature of matter
1. Take about 50 cm3 water in a 100 cm3 beaker.
2. Mark the level of water.
3. Add some sugar to the beaker and stir with the help of a glass rod.
4. Observe the change in water level.
Fig. 4.1. Dissolution of sugar in water. In solution particles of sugar are present in the spaces between particles of water
It is observed that the crystals of sugar disappear. The level of water remains unchanged. These observations can be explained by assuming that matter is made up of small particles. On dissolution, the particles of sugar get distributed into the spaces between particles of water.
• The constituent particles of matter are extremely small in size
The following activity demonstrates that the constituent particles of matter are very small
ACTIVITY 4.2
To demonstrate that the particles of matter are very small
1. Take a 250 cm3 beaker and add 100 cm3 water to it
2. Now add 2-3 crystals of KMnO4 and stir with a glass rod in order to dissolve the crystals.
3. Take 10 cm3 of this solution and add to 100 cm3 of water taken in another beaker.
4. Take 10 cm3 of this diluted solution and put into 100 cm3 of water taken in still another beaker.
5. Repeat this process 10 times. Observe the colour of the solution in the last beaker.
It is observed that the water in the last beaker is still coloured but the intensity of colour becomes light It indicates that KMnO4 crystal contains millions of tiny particles, some of which are still present even in the last beaker after so much dilution.
• There are spaces between particles of matter In activity 4.1 we observed that when sugar is dissolved in water, the volume of the liquid remains unchanged. During dissolution, the particles of sugar get into the spaces between the particles of water. As a result, they get evenly Distributed and there is no noticeable change in volume. Similarly, when KMnO4 is dissolved in water, its particles get evenly distributed throughout the bulk of water. This is indicated by uniform colour of the solution. This indicates that there are spaces between particles of matter. The particles of KMnO4 get uniformly distributed in the spaces between water molecules.
• The particles of matter are continuously moving The motion of particles of matter can be demonstrated by the following practical activities:
ACTIVITY 4.3
To demonstrate motion of particles of matter
Place a bottle containing concentrated aqueous solution of ammonia in a corner of the room. Remove the stopper.
What do you observe?
It is observed that ammoniacal smell can be sensed sitting at a distance.
It demonstrates that the particles of ammonia are moving. Due to this motion they are able to reach the observer.
Similarly, if an incense stick is lighted and placed in one comer of a room, its pleasant smell spreads in the whole room quickly. It demonstrates that the particles of matter possess motion. A burning incense stick produces some gases (vapour) having pleasant smell. The particles of these gases due to motion spread in the entire room and their presence can be felt by sensing the smell.
ACTIVITY 4.4
To demonstrate motion of particles in water and ink
1. Take a 250 cm3 beaker and add about 100 cm3 of water to it.
2. Put a drop of blue ink to the water taken in the beaker. What do you observe?
It is observed that the blue ink gets evenly distributed in the water.
This demonstrates that the particles of water and ink possess motion.
Due to motion of the particles, the particles of the two liquids are able to mix with each other.
ACTIVITY 4.5
To demonstrate that the kinetic energy of particles increases with increase in temperature
1. Take two beakers. To one beaker add 100 cm3 of cold water and to the other beaker add 1 00 cm3 of hot water.
2. Now add a crystal of potassium permanganate to both the beakers.
What do you observe?
It is observed that the purple colour of potassium permanganate starts spreading and after sometime the entire solution becomes purple. The rate of mixing is faster in case of hot water. This experiment demonstrates that the particles of matter possess motion and that the kinetic energy of the particles increases with increase in temperature
The above activities demonstrate that when two different forms of matter are brought in contact they intermix spontaneously. This intermixing is possible due to motion of the particles of matter and also due to the spaces between them. The intermixing takes place due to movement of particles of one form into the spaces between the particles of the other form of matter. This spontaneous intermixing of particles of two different types of matter is called diffusion. The rate of diffusion becomes faster with increase in temperature because at higher temperature, the particles have more energy and hence move faster.
• Particles of matter attract each other
There are forces of attraction between particles of matter. The evidence for forces of attraction in gases is obtained from the fact that they can be liquefied by applying pressure.
The important characteristics of particles of matter are summarized below:
1. The particles of matter are extremely small in size.
2. The particles of matter have spaces between them.
3. The particles of matter are continuously moving.
4. The particles of matter attract each other.
The constituent particles of matter may be atoms, molecules or ions. Some examples are given below in tabular form:
Constituent particles Examples
1. Atoms Argon, neon, helium, diamond
2. Molecules Sucrose , glucose,urea,methane carbon(IV) oxide
3. Ions Sodium chloride, magnesium oxide, zinc sulphide
STATES OF MATTER
Matter can be classified into three categories depending upon its physical state, namely: solids, liquids and gases. These states of matter arise due to variation in the characteristics of the particles of matter.
PROPERTIES OF SOLIDS
(i) The matter in solid state possesses a definite volume, a definite shape, distinct boundaries and a definite mass.
(ii) Solids are rigid and almost incompressible.
(iii) Solids may break under force but it is difficult to change their shape.
(iv) Solids generally possess high densities.
(v) Solids do not exhibit diffusion. Some common examples are: table, chair, common salt, silver, ice, diamond, etc.
PROPERTIES OF LIQUIDS
(i) The matter in liquid state possesses a definite volume, a definite mass, but no definite shape.
(ii) Liquids are also almost incompressible but are not rigid. In fact, they can flow and acquire the shape of the container in which they are kept.
(iii) Liquids can undergo diffusion.
(iv) Liquids also have high densities but less than that of solids.
Some examples are: milk, water, alcohol, petrol, kerosene, fruit juices, etc.
PROPERTIES OF GASES
(i) The matter in gaseous state has neither definite volume nor definite shape but it has definite mass. It acquires the shape and volume of the container.
(ii) Gases are highly compressible. For example, natural gas in compressed form is used as fuel (Compressed Natural Gas-CNG) in internal combustion engines. Oxygen supplied to hospitals in cylinders is also in compressed form. Due to high compressibility large volumes of gas can be compressed into a small cylinder and transported easily.
(iii) The gases exhibit the property of diffusing very fast into other gases.
(iv) Gases exert pressure on the walls of the container in which they are stored.
(v) Gases have very low densities.
Some common examples of gases are: air, hydrogen carbon(IV) oxide, hydrogen, sulphide, ammonia, oxygen, nitrogen, etc.
- In solids, the interparticle spaces are small. They have smaller amounts of energy than the same particles in the liquid and gaseous states. Consequently, the particles in solid state cannot overcome the strong forces of attraction which are holding them together. In solids, particles can only vibrate about fixed positions. Thus, particles in a solid have vibrational and rotational motion but no translational motion. Because of smaller interparticle spaces, solids are almost incompressible while due to absence of translational motion they are rigid.
- In liquids, interparticle spaces are somewhat larger than in solids and the particles have larger amounts of energy. The particles in liquids can overcome the interparticle forces between each other to some extent and hence can move freely. However, the intermolecular forces in liquids are strong enough to keep the particles within the bulk. The particles in liquid state possess vibrational, rotational and translational motion.
- In gases, the interparticle spaces are very large and the particle possess much larger amounts of energy than those in solids and liquids. The gas particles have sufficient energy to overcome the interparticle attractive forces almost completely. As a result the gas particles move rapidly and randomly into any space available to them. Thus, a gas fills completely the vessel in which it is kept. That is why gases have neither definite shape nor definite volume. Since particles in gaseous state are free to move, they collide with one another and also against walls of the container. The pressure of the gas is due to collisions of molecules against walls of the container.
- Solid and liquid states are known as condensed states of matter due to smaller interparticle spaces” and negligible compressibility.
- Liquids and gases are known as fluids because of their ability to flow and take the shape of container
PLASMA STATE-The Fourth State of matter
The matter in this state is in the form of ionized gas. It consists of neutral mixture of positive ions and unbound electrons. The matter exists in this state at temperatures in the range 10000°C to 15000°C. The matter in the sun and stars exists in plasma state. It is estimated that 99% of the matter in the universe exists in plasma state. Neon in neon lights is also in plasma state.
| Plasma has neither a definite volume nor a definite shape. Plasma often is seen in ionized gases. Plasma is distinct from a gas because it possesses unique properties. Free electrical charges (not bound to atoms or ions) cause plasma to be electrically conductive. Plasma may be formed by heating and ionizing a gas. |
Why Solids, Liquids and Gases Exhibit Different Properties?
The properties of matter in the three states of matter are different because the characteristics of the particles vary in the three states of matter.
Now let us understand how the characteristics of particles vary in the three states of matter.
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