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.

See also  NAMES OF LABORATORY APPARATUS

(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.

 

PROPERT ES 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

  • 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.

 

 

A comparison of the characteristic properties of solids,  liquids and gases are given in Table 4.1.

 

Table 4.1. Comparison of Characteristic Properties of Solids, Liquids and Gases

Property                      Solids                          Liquids                        Gases

l.Sbape                        Definite                       Take the shape           Take the shape of

of the con                    the container by

tainer, but do               occupying whole

not necessarily             of the space avaoccupy

all of it.                        ilable to them.

 

  1. Volume                   Definite                      Definite                      Take the volume

of the container.

 

  1. Compre-                  Almost            nil                   Almost nil                   Very large.

ssibility

 

  1. Fluidity or               Rigid                           Fluid                                        Fluid

Rigidity

 

  1. Density                    Large                           Large                           Very small.

 

  1. Diffusion                 Generally                    Diffuse slowly            Diffuse rapidly.

do not

diffuse

 

  1. Free                         Any                             Only one free              No free surface.

Surfaces                      number of                               surface

free

surfaces

 

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.

 

Changes in states

Chemical properties: Properties that do change tha chemical nature of matter

Examples of physical properties are: color, smell, freezing point, boiling point, melting point, infra-red spectrum, attraction (paramagnetic) or repulsion (diamagnetic) to magnets, opacity, viscosity and density. There are many more examples. Note that measuring each of these properties will not alter the basic nature of the substance.

Examples of chemical properties are: heat of combustion, reactivity with water, PH, and electromotive force.

The more properties we can identify for a substance, the better we know the nature of that substance. These properties can then help us model the substance and thus understand how this substance will behave under various conditions.

Physical and Chemical Properties

All substances have properties that we can use to identify them. For example we can idenify a person by their face, their voice, height, finger prints, DNA etc.. The more of these properties that we can identify, the better we know the person. In a similar way matter has properties – and there are many of them. There are two basic types of properties that we can associate with matter. These properties are called Physical properties and Chemical properties:

Physical properties: Properties that do not change the chemical nature of matter
Chemical properties: Properties that do change tha chemical nature of matter

Examples of physical properties are: color, smell, freezing point, boiling point, melting point, infra-red spectrum, attraction (paramagnetic) or repulsion (diamagnetic) to magnets, opacity, viscosity and density. There are many more examples. Note that measuring each of these properties will not alter the basic nature of the substance.

Examples of chemical properties are: heat of combustion, reactivity with water, PH, and electromotive force.

The more properties we can identify for a substance, the better we know the nature of that substance. These properties can then help us model the substance and thus understand how this substance will behave under various conditions.

Changing States of Matter

A material will change from one state or phase to another at specific combinations of temperature and surrounding pressure. Typically, the pressure is atmospheric pressure, so temperature is the determining factor to the change in state in thosecases.

Names such as boiling and freezing are given to the various changes in states of matter. The temperature of a material will increase until it reaches the point where the change takes place. It will stay at that temperature until that change is completed.

                              

Changes in states

The states of matter are solid, liquid, gas and plasma. Since there is some debate on whether plasma should be classified as a state of matter and since it is not commonly experienced, we will not discuss its properties here.

Order of changes

When heat is applied to a material, its change in state typically goes from solid to liquid to gas. There are some exceptions where the material will go directly from a solid to a gas.

When a material is cooled, its change in state typically goes from gas to liquid to solid. There are some exceptions where the material will go directly from a gas to asolid.

Names of changes

Each change in the state of matter has a specific name.

 

Start from:

Change to:

Name

solid liquid melting
liquid solid freezing
liquid gas boiling
gas liquid condensation
solid gas
(skipping liquid phase)
sublimation
gas solid
(skipping liquid phase)
deposition

Change in temperature

When a material reaches the temperature at which a change in state occurs, the temperature will remain the same until all the energy is used to change the state.

Melting

When a solid is heated, its temperature rises until it reaches its melting point. Any additional heat added to the material will not raise the temperature until all of the material is melted.

Thus, if you heat some ice, its temperature will rise until it reaches 0° C (32° F). Then the ice will stay at that temperature until all the ice is melted. The heat energy is used to melt the ice and not to raise the temperature. After the ice is melted, the temperature of the water will continue to rise as more heat is applied.

Boiling

When a liquid is heated, its temperature rises until it reaches its boiling point. The temperature will then remain at that point until all of the liquid is boiled away.

For example, the temperature of a pot of water will increase until it reaches 100° C (212° F). It will stay there until all the water is boiled away. The temperature of the steam can then be increased.

Cooling

Likewise, when a gas is cooled, its temperature will drop until it reaches the condensation point. Any additional cooling or heat loss will not lower the temperature until all of the gas is condensed into the liquid state.

Then the temperature of the liquid will continue to drop as more cooling is applied. Once the liquid reaches the freezing point, the temperature will remain at that point until all of the liquid is solidified. Then the temperature of the solid cancontinue to decrease.

Chemical Changes

Chemical changes take place on the molecular level. A chemical change produces a new substance. Examples of chemical changes include combustion (burning), cooking an egg, rusting of an iron pan, and mixing hydrochloric acid and sodium hydroxide to make salt and water.

Physical Changes

Physical changes are concerned with energy and states of matter.

 

A physical change does not produce a new substance. Changes in state or phase (melting, freezing, vaporization, condensation, sublimation) are physical changes. Examples of physical changes include crushing a can, melting an ice cube, and breaking a bottle.

How to Tell Chemical & Physical Changes Apart

A chemical change makes a substance that wasn’t there before. There may be clues that a chemical reaction took place, such as light, heat, color change, gas production, odor, or sound. The starting and ending materials of a physical change are the same, even though they may look different.

Examples of Chemical Changes

  • burning wood
  • dissolving salt in water
  • mixing acid and base
  • digesting food

Examples of Physical Changes

  • crumpling a sheet of paper
  • melting an ice cube
  • casting silver in a mold
  • breaking a bottle

How to Tell?

Look for an indication that a chemical change occurred. Chemical reactions release or absorb heat or other energy or may produce a gas, odor, color or sound. If you don’t see any of these indications, a physical change likely occurred.

In some cases, it may be hard to tell whether a chemical or physical change occurred. For example, when you dissolve sugar in water, a physical change occurs. The form of the sugar changes, but it remains the same chemically (sucrose molecules). However, when you dissolve salt in water the salt dissociates into its ions (from NaCl into Na+ and Cl) so a chemical change occurs. In both cases a white solid dissolves into a clear liquid and in both cases you can recover the starting material by removing the water, yet the processes are not the same.

Difference between chemical and physical change

 

Chemical change is any change that results in the formation of new chemical substances. At the molecular level, chemical change involves making or breaking of bonds between atoms. These changes are chemical:

·         iron rusting (iron oxide forms)

·         gasoline burning (water vapor and carbon dioxide form)

·         eggs cooking (fluid protein molecules uncoil and crosslink to form a network)

·         bread rising (yeast converts carbohydrates into carbon dioxide gas)

·         milk souring (sour-tasting lactic acid is produced)

·         suntanning (vitamin D and melanin is produced)

Physical change rearranges molecules but doesn’t affect their internal structures. Some examples of physical change are:

·         whipping egg whites (air is forced into the fluid, but no new substance is produced)

·         magnetizing a compass needle (there is realignment of groups (“domains”) of iron atoms, but no real change within the iron atoms themselves).

·         boiling water (water molecules are forced away from each other when the liquid changes to vapor, but the molecules are still H2O.)

·         dissolving sugar in water (sugar molecules are dispersed within the water, but the individual sugar molecules are unchanged.) dicing potatoes (cutting usually separates molecules without changing them.)

 

 

SUMMARY

  • Matter is anything that occupies space and has mass.
  • Matter can be classified as solids, liquids and gases on the basis of its physical state.
  • Matter is made up of extremely small particles.
  • There are spaces between particles of matter.
  • The particles of matter are continuously moving.
  • The particles of matter attract each other.
  • The spaces between particles are minimum in solid state and maximum in gases.
  • The kinetic energy of particles minimum in solid state and maximum in gaseous state.
  • The force of attraction between particles is maximum in solid state and negligible in gaseous state.
  • Liquids and gases exhibit diffusion because their particles possess translatory motion and possess larger interparticle spaces.
  • Solid and liquid states are known as condensed states of matter due to smaller interparticle spaces and very little compressibility.
  • Liquids and gases are known as fluids because of their ability to flow and take the shape of the container.

 

EVALUATION

1.Which of the following is not an example of matter?

(a) Air                          (b) Almonds

(c) Cold-drink             (d) Love.

 

  1. Which of the following has the strongest interparticle forces?

(a) Nitrogen                 (b) Water

(c) Iron                        d) Neon.

 

3 Which of the following has atoms as the constituent particles?

(a) Dry ice                   (b) Argon

(c) Glucose                  (d) Potassium chloride.

 

Fill in the blanks

Complete the following sentences by supplying appropriate words:

(i) The particles in …… state do not possess translator motion.

(ii) …… and …… states of matter are known as fluid states of matter.

(iii) Particles in …… state possess maximum kinetic energy.

(iv) Kinetic energy of particles of matter …… with increase in temperature.

 

I .Discussion Question

5 What are the characteristics of the particles of matter?

  1. Which out of iron and chalk has stronger interparticle forces?
  2. Give reasons for the following observations:

We can get the smell of perfume sitting from several meters away.

  1. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
  2. Describe an activity to demonstrate that the matter consists of particles and that the particles are of extremely small size.
  3. What are the characteristics of matter in solid state?

11.P Explain why:

(i) Solids do not undergo diffusion whereas liquids and gases undergo diffusion readily.

(ii) Gases are highly compressible.

  1. Give reasons for the following:

(i) A gas fills completely the vessel in which it is kept.

(ii) A gas exerts pressure on the walls of the container.

  1. Explain why solid and liquid states are known as condensed states of matter.
  2. Give reasons:

(i) Sponge is a solid yet we are able to compress it.

(ii) Sugar when kept in jars of different shapes it takes the shape of the jar yet we call it a solid.

15.With two examples in each case,mention physical and chemical processes in your environment.

16.What are states of matter?Use a suitable diagram to show how one state can be converted to another state.

 

See also

Chemistry as a Subject

STRUCTURE OF THE ATOM

ATOMIC NUMBER

NOMENCLATURE OF CHEMICAL COMPOUNDS

PARTICULATE NATURE OF MATTER

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