Matter In Our Surrounding

Matter is anything that occupies space and has mass.

Hydrogen, oxygen, sugar, sand, air and water are examples of matter.

In early times, Greek and Indian thinkers explained matter through basic elements.

Greek philosophers classified matter into four basic elements:

• Fire
• Water
• Air
• Earth

Indian philosophers classified matter into five basic elements:

• Fire
• Water
• Air
• Earth
• Sky

In modern science, matter is classified in two main ways:

• Physical classification – based on physical properties of matter
• Chemical classification – based on chemical composition of matter

Physical Nature Of Matter

Matter is made up of extremely small particles.

These particles are so tiny that they are beyond normal imagination.

Every substance around us is made of these minuscule particles.

Characteristics Of Particles Of Matter

Particles of matter have some important characteristics.

• Particles of matter have spaces between them.
• This explains why one substance can dissolve in another.
• Particles of matter are continuously moving.
• Particles of matter attract each other.
• To break a substance, we need to overcome this force of attraction.

States Of Matter

Matter can be classified on the basis of interparticle forces and the arrangement of particles.

The three main states of matter are:

• Solid
• Liquid
• Gas

These states are interconvertible.

They can change from one state to another by changing:

• Temperature
• Pressure

Example:
Ice can be converted from solid to liquid by increasing temperature.

Fourth And Fifth States Of Matter

Apart from solid, liquid and gas, two more states of matter are also discussed.

• Plasma
• Bose-Einstein Condensate

Plasma is called the fourth state of matter.

Bose-Einstein Condensate is called the fifth state of matter.

Properties Of Solids, Liquids And Gases

The space between two particles is called intermolecular space.

The energy possessed by particles due to motion is called kinetic energy.

Comparison Of Solid, Liquid And Gas

Property	Solid	Liquid	Gas
Particles	Tightly packed	Loosely packed	Independent
Shape	Fixed	Not fixed	Not fixed
Volume	Fixed	Fixed	Not fixed
Rigidity	High	Less	Negligible
Force of attraction	Strongest	Intermediate	Weakest
Fluidity	No	Yes	Yes
Compressibility	No	Slight	High
Density	High	Low	Very low
Diffusibility	No	Less	High
Kinetic energy	Low	Intermediate	High
Examples	Crystalline and amorphous solids	All fluids	O₂, CO₂, SO₂, NO₂

Solid State

In solids, particles are closely packed.

Because of close packing, solid particles do not move freely. They only vibrate about their fixed positions.

This means solids mainly show vibratory motion.

Due to very little movement of particles, solids usually do not diffuse into other solids.

However, rare examples of solid-solid diffusion are possible.

Rare Examples Of Solid Diffusion

• A blackboard on which something is written with chalk becomes difficult to clean if left for 15-20 days.
• When two blocks of metal are tightly bound together and left undisturbed for a few years, pure gold may diffuse into pure lead.

Diffusion

Diffusion is the phenomenon in which particles of matter intermix on their own with each other.

The rate of diffusion follows this order:

• Gases – highest
• Liquids – lower than gases but higher than solids
• Solids – very low

Example:

• Spreading of ink in water

Cause Of Diffusion

During diffusion, particles move into the interparticle spaces of another substance.

When temperature increases, kinetic energy of particles also increases.

As a result, the rate of diffusion increases.

Can Matter Change Its State?

A substance may exist in solid, liquid or gas state depending on temperature and pressure.

When temperature is increased at constant pressure:

• Kinetic energy of particles increases.
• Particles vibrate with higher energy.
• Interparticle force of attraction becomes weaker.
• Particles detach from their fixed positions.
• They begin to move freely.

A solid usually changes into a liquid on heating.

On further heating, the liquid changes into gas.

On cooling, a gas condenses into liquid.

On further cooling, the liquid changes into solid.

The general change is:

• Solid ⇌ Liquid ⇌ Gas
• Heating changes solid to liquid and liquid to gas.
• Cooling changes gas to liquid and liquid to solid.

Melting Point

The melting point is the temperature at which a solid melts to become liquid at atmospheric pressure.

The melting point of ice is 0°C.

The process of melting is also called fusion.

At the melting point, solid and liquid phases exist together in equilibrium.

Nuclear Fusion

When two hydrogen atoms combine to form one helium atom, the process is called nuclear fusion.

A large amount of energy is produced during fusion.

Scales Of Measuring Temperature

Temperature can be measured on different scales.

Important formulas are:

• K = °C + 273
• °F = 9/5 × °C + 32°

Example:
450 K can be written in Celsius as:

• °C = 450 – 273
• °C = 177°C

Boiling Point

The boiling point is the temperature at which a liquid changes into gas.

Boiling is a bulk phenomenon.

It may also be defined as the temperature at which the vapour pressure of a liquid becomes equal to atmospheric pressure.

Latent Heat

The heat energy required to change the state of a substance is called latent heat.

During a change of state, the temperature does not increase even though heat is supplied.

This is because the heat supplied is used to overcome the forces of attraction between particles.

Latent Heat Of Fusion

Latent heat of fusion is the amount of heat energy required to change 1 Kg of a solid into liquid at atmospheric pressure without any change in temperature at its melting point.

Latent Heat Of Vapourisation

Latent heat of vapourisation is the amount of heat energy required to change 1 Kg of a liquid into gas at atmospheric pressure without any change in temperature at its boiling point.

Sublimation

Sublimation is the direct change of a substance from solid state to gaseous state without changing into liquid state.

Examples:

• Camphor
• Iodine
• Dry ice

Solid carbon dioxide is known as dry ice.

Effect Of Pressure On Matter

When pressure is applied, the interparticle spaces between particles of matter decrease.

At low temperature and high pressure, a gas can be liquefied.

The conversion of gas into liquid by increasing pressure or decreasing temperature is called liquefaction.

This is why large volumes of gases can be compressed into small cylinders.

Example:

• Compressed Natural Gas, or CNG

Evaporation

Evaporation is the phenomenon in which a liquid changes into vapour at any temperature below its boiling point.

Evaporation is a surface phenomenon.

It is slower than boiling and can occur at all temperatures.

Factors Affecting Rate Of Evaporation

The rate of evaporation increases when:

• Surface area of liquid increases.
• Temperature increases.
• Wind speed increases.

The rate of evaporation decreases when:

• Humidity increases.

Evaporation Causes Cooling

During evaporation, particles of a liquid absorb energy from the surroundings.

This energy helps them overcome interparticle forces of attraction and change into vapour.

Since heat is absorbed from the surroundings, the surroundings become cool.

Applications Of Evaporation

Evaporation is useful in daily life.

• Water remains cool in earthen pots because water evaporates through tiny pores.
• Sweating keeps our body cool because sweat evaporates and removes heat from the body.
• Cotton clothes are worn in summer because they absorb sweat and help evaporation.
• Water droplets are seen on the outer surface of a glass containing ice-cold water because water vapour from air condenses on the cold surface.
• Wet cloth strips are placed on the forehead during high fever because evaporation removes heat from the body.

Plasma

Plasma is a high-energy gaseous state of matter.

It is the fourth state of matter.

Features Of Plasma

• It is a high-energy state.
• It is very unstable.
• Its particles move extremely fast.
• It exists under extremely high temperature conditions.

Bose-Einstein Condensate

Bose-Einstein Condensate is the fifth state of matter.

It is formed when a dilute gas of bosons is cooled to a temperature very close to absolute zero.

Absolute zero is:

• 0 Kelvin
• -273.15°C

Examples include:

• Helium-4
• Rubidium-87 atoms
• Photons

Important Conceptual Points

• Kinetic energy of particles is directly proportional to temperature.
• Ice has less kinetic energy than water and steam.
• Steam at 100°C has more kinetic energy than water at 100°C.
• Interparticle force of attraction is strongest in solids and weakest in gases.
• Interparticle space is least in solids and maximum in gases.
• Increasing order of force of attraction is: Gas < Liquid < Solid.
• Increasing order of randomness is: Solid < Liquid < Gas.
• Gases are highly compressible because their particles have large spaces between them.
• Liquids have fixed volume but no fixed shape.
• Gases have neither fixed shape nor fixed volume.
• Gases and liquids are called fluids because they can flow.
• Ice floats on water because ice has lower density than water.
• At high altitudes, cooking becomes difficult because the boiling point of water decreases.

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