Matter is anything that has mass and occupies space. Air, water, rocks, books, plants, animals, and the human body are all made of matter.
Matter is composed of extremely small units called constituent particles. Depending on the substance, these particles may be atoms, molecules, or ions. They are too small to be seen with the naked eye.
Main Features of Particles of Matter
Activity 1: Breaking Chalk
Break a piece of chalk into smaller pieces and grind one piece into powder. Each grain remains chalk because only its size changes; no new substance is formed. Grinding chalk is therefore a physical change.
Even the smallest visible grain consists of many much smaller constituent particles. This activity demonstrates that a large piece of matter is made of numerous tiny particles.
Activity 2: Dissolving Sugar in Water
Add sugar to clean drinking water and stir until it dissolves. The sugar is no longer visible, but the water tastes sweet. The sugar has not disappeared. Its particles have separated, spread throughout the water, and occupied spaces between water particles.
This activity shows that:
Safety note: Taste only mixtures prepared with clean, edible materials. Never taste laboratory chemicals.
Interparticle space is the space between neighbouring particles of a substance. It is smallest in most solids, greater in liquids, and greatest in gases.
Interparticle attraction is the force that holds particles together. The strength of this force depends on the substance and the distance between its particles. Particles that are close together generally attract one another more strongly than particles that are far apart.
The balance between the movement of particles, the spaces between them, and their forces of attraction helps determine whether a substance exists as a solid, liquid, or gas.
The three common states of matter are solid, liquid, and gas.
|
Property |
Solid |
Liquid |
Gas |
|
Shape |
Definite |
No definite shape; takes the container’s shape |
No definite shape; fills the container |
|
Volume |
Definite |
Definite |
No definite volume |
|
Particle arrangement |
Very closely packed, usually orderly |
Close together but irregular |
Very far apart and random |
|
Particle movement |
Vibrate about fixed positions |
Move and slide past one another |
Move rapidly and freely |
|
Interparticle attraction |
Strongest |
Weaker than in solids |
Very weak or negligible |
|
Interparticle space |
Least |
Moderate |
Greatest |
|
Compressibility |
Negligible |
Very low |
High |
|
Ability to flow |
Does not flow |
Flows |
Flows |
|
Examples |
Ice, sugar, wood, stone |
Water, milk, oil |
Oxygen, nitrogen, carbon dioxide |
Liquids and gases can flow and are therefore collectively called fluids.
3.1 Solid State
The particles of a solid are closely packed and held by strong forces of attraction. They remain in nearly fixed positions and can only vibrate. Consequently, a solid has a definite shape and volume and is difficult to compress.
Activity 3: Observing Solids
Observe objects such as an iron nail, stone, key, wood, or rock salt. Each object retains its shape and volume. Their rigidity indicates that their particles are strongly held together.
3.2 Liquid State
Particles in a liquid remain fairly close, but the forces between them are weaker than in a solid. They can move and slide past one another. Thus, a liquid has a definite volume but no definite shape; it takes the shape of its container.
Activity 4: Transferring Water
Pour the same measured quantity of water into containers of different shapes. The shape of the water changes in each container, but its volume remains almost the same if none is spilled. This confirms that liquids have a definite volume but no fixed shape.
3.3 Gaseous State
Gas particles are far apart and experience very weak forces of attraction. They move rapidly and freely in all directions. A gas therefore has neither a definite shape nor a definite volume and expands to fill all available space.
Activity 5: Spreading Through Gas Jars
When air containing a little visible smoke is allowed to enter another gas jar, it gradually spreads through the available space. This illustrates the continuous random movement of gas particles.
Safety note: Any demonstration involving smoke, flame, heated materials, or glassware must be performed by a teacher or responsible adult in a well-ventilated place. Smoke itself consists of fine solid and liquid particles suspended in gases; it is used only to make movement visible.
Particles of matter possess kinetic energy because they are continuously moving. Heating increases this energy, making the particles move or vibrate faster. As their movement increases, they may partially or completely overcome the attractive forces holding them together.
4.1 Melting
When a solid is heated, its particles vibrate more rapidly. At a particular temperature, they gain enough energy to leave their fixed positions and move past one another. The solid then changes into a liquid.
The melting point is the temperature at which a solid changes into a liquid at atmospheric pressure.
Different solids have different melting points because the forces holding their particles together differ in strength. Ice is unusual because its particles are arranged farther apart than they are in liquid water.
4.2 Boiling
When a liquid is heated, its particles move faster. At the boiling point, particles throughout the liquid gain enough energy to escape into the gaseous state. Rapid vapour formation produces bubbles within the liquid.
The boiling point is the temperature at which a liquid changes rapidly into vapour throughout its mass at atmospheric pressure.
4.3 Evaporation
Evaporation is the slow change of a liquid into vapour from its surface. It can occur at temperatures below the boiling point. Unlike boiling, evaporation occurs only at the surface and does not produce bubbles throughout the liquid.
Changes of State
Solid —(heating/melting)→ Liquid —(heating/boiling)→ Gas
During these changes, the substance remains chemically the same; only the arrangement, movement, and energy of its particles change.
Activity 6: Compressing Air in a Syringe
Trap air in a needle-free syringe by closing its opening and gently pushing the plunger. The air volume decreases because its particles are far apart and can be forced closer together. When the pressure is released, the particles spread out again.
Water is far less compressible because its particles are already much closer together. Solids are also difficult to compress because their particles are very closely packed.
Safety note: Use only a needle-free syringe and push the plunger gently. Never point it toward anyone.
Activity 7: Sugar and Water Levels
Mark the level of water in a transparent container. Add sugar and note the temporary rise in level. After stirring, the sugar dissolves and the final volume may be less than the separate volumes of the sugar and water added together. Sugar particles enter spaces between the water particles.
Soluble substances such as sugar, salt, and glucose dissolve in water. Insoluble substances such as sand do not dissolve; their visible particles settle and occupy additional space.
Even solids contain interparticle spaces, although these spaces are very small. They are not necessarily filled with air.
Diffusion is the spontaneous movement and mixing of particles from a region of higher concentration to a region of lower concentration. It occurs because particles are continuously moving.
Diffusion is usually fastest in gases, slower in liquids, and extremely slow in solids because the freedom of particle movement differs in each state.
Activity 8: Colour Spreading in Water
When a tiny crystal of potassium permanganate is placed in water, purple streaks gradually spread until the water becomes uniformly coloured. The dissolved particles mix with the continuously moving water particles.
If equal-sized crystals are placed separately in hot, room-temperature, and cold water, the colour spreads fastest in hot water and slowest in cold water. Heating increases the kinetic energy and speed of the particles, so diffusion occurs more rapidly.
Safety note: Potassium permanganate must be handled under teacher supervision. Avoid skin and eye contact, and never taste the solution.
Activity 9: Fragrance Spreading Through Air
The fragrance from an incense stick or perfume is first strongest near its source. After some time, it can be detected farther away because fragrance particles diffuse through the moving particles of air.
Other examples of diffusion include the smell of food spreading through a house and a drop of ink slowly spreading through water.
A soluble substance dissolves in a particular liquid. Its particles separate and become distributed among the particles of the liquid. Sugar and common salt are soluble in water.
An insoluble substance does not dissolve appreciably in a particular liquid. Sand is insoluble in water and usually settles at the bottom.
Whether a substance dissolves depends on the nature of both the substance and the liquid. Dissolving should not be confused with melting: dissolving involves one substance mixing uniformly with another, whereas melting is a change from solid to liquid caused by heating.
In this chapter, a constituent particle means an extremely small unit, such as an atom, molecule, or ion, that makes up matter.
In air pollution, suspended particulate matter (SPM) refers to tiny pieces of dust, soot, smoke, or liquid droplets suspended in air. These particles are much larger than atoms and molecules and are themselves made of many constituent particles.
The ancient Indian philosopher Acharya Kanada proposed that matter was composed of extremely small, indivisible particles called parmanu. He presented his ideas in the Vaisheshika Sutra, an important early attempt to explain the particulate nature of matter.
Matter has mass and occupies space. It is made of extremely small particles that have spaces between them, move continuously, and attract one another. In solids, the particles are closely packed and strongly held, giving solids a definite shape and volume. In liquids, the particles can move past one another, so liquids flow and take the shape of their container while retaining a definite volume. Gas particles are far apart and move freely, so gases have neither a definite shape nor a definite volume.
Heating increases particle movement. A solid may melt into a liquid, and a liquid may boil or evaporate into a gas. Particles also mix through diffusion, which occurs faster at higher temperatures. These ideas form the particle model of matter and explain many everyday observations.
|
Term |
Meaning |
|
Matter |
Anything that has mass and occupies space |
|
Constituent particle |
A basic microscopic unit that makes up a substance |
|
Interparticle space |
Space between neighbouring particles |
|
Interparticle attraction |
Force of attraction between particles |
|
Solid |
State with a definite shape and definite volume |
|
Liquid |
State with a definite volume but no definite shape |
|
Gas |
State with neither a definite shape nor a definite volume |
|
Fluid |
A substance that can flow; liquids and gases are fluids |
|
Melting point |
Temperature at which a solid changes into a liquid |
|
Boiling point |
Temperature at which a liquid boils and changes into vapour |
|
Evaporation |
Slow formation of vapour from a liquid’s surface |
|
Diffusion |
Movement and mixing of particles from higher to lower concentration |
|
Soluble |
Able to dissolve in a particular solvent |
|
Insoluble |
Unable to dissolve appreciably in a particular solvent |
Answer: Yes. Every speck of the powder is still chalk. Grinding changes only the size and shape of the chalk; it does not produce a new substance. Therefore, grinding chalk is a physical change.
Answer: No. Even the tiny pieces of chalk are made up of much smaller constituent particles. These particles are the basic units that make up the chalk.
Answer: No. A gas has neither a fixed shape nor a fixed volume. Its particles are far apart and move freely in all directions. Therefore, a gas spreads out and occupies all the available space in its container.
Answer: Water attracts and separates the constituent particles of sugar. These particles spread throughout the water and occupy spaces between the water particles, forming a solution. Sand particles are not sufficiently attracted to water and therefore do not dissolve. They remain separate and eventually settle at the bottom.
The main difference between solids and liquids is that their constituent particles are:
Answer:Option 4 is correct. In solids, particles are closely packed and remain in nearly fixed positions. In liquids, particles remain close together but can move past one another.
Answer:Option 3 is correct. A chair is entirely made of constituent particles. If every particle were removed, no material would remain to give the chair its mass, shape, or structure.
Answer: Gas particles are far apart, experience very weak forces of attraction, and move rapidly in all directions. They therefore diffuse and mix easily. The particles of a solid are closely packed and held in nearly fixed positions by strong forces of attraction, so solids do not mix by diffusion under ordinary conditions.
Answer: Milk is a liquid. Its particles can move past one another, so it flows and spreads over the table. The tumbler is a solid. Its particles are tightly packed and held in fixed positions, so it retains its definite shape.
Answer:
Ice (solid) → Water (liquid) → Water vapour (gas)
|
State |
Particle arrangement |
Particle movement |
|
Ice |
Very closely packed in an orderly arrangement |
Vibrate about fixed positions |
|
Water |
Close together but irregularly arranged |
Move and slide past one another |
|
Water vapour |
Very far apart and randomly arranged |
Move rapidly and freely in all directions |
On heating, the particles gain kinetic energy. During melting, they leave their fixed positions and form liquid water. With further heating, they move farther apart and escape as water vapour.
Answer:
Answer:
Match each part of the candle with the particle diagram showing the corresponding solid, liquid, or gaseous arrangement.
Answer: Ocean water contains dissolved salts, mainly sodium chloride. When salt dissolves, its particles separate and spread uniformly through the water. These particles are too small to be seen with the naked eye, but they produce the salty taste.
Answer: Rice grains and rice flour are solids. Each individual grain or flour particle has a definite shape and volume. A collection of these particles can be poured and can take the overall shape of a container because the separate solid particles move past one another. This behaviour does not make them liquids.
Activity: Spreading of fragrance
Light an incense stick in one corner of a room, wait for a few minutes, and observe whether its fragrance can be detected from a distance.
Observation: At first, the smell is stronger near the incense stick. After some time, it can be detected in other parts of the room.
Conclusion: Fragrant vapour particles mix with the particles of air and move from a region of higher concentration to regions of lower concentration. This spreading of particles is called diffusion. It shows that gas particles are continuously moving and have spaces between them.
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