Matter | ICSE Class 6 Chemistry Notes

This note covers matter, mass and volume, solids, liquids and gases, particle spacing and attraction, particle motion, changes of state, expansion and contraction, and physical and chemical changes caused by heating.

What is matter, and how do mass and volume describe it?

Definition: Matter is anything that has mass and occupies space. Mass measures the quantity of matter in an object. Volume is the space occupied by matter.

Water, sand, pebbles and a cup are examples of matter. They differ in their properties, meaning observable or measurable characteristics, but each has mass and occupies space. The word matter therefore includes many different materials rather than naming one particular material.

How are mass and volume different?

Mass answers the question of how much matter an object contains. Gram, written as g, and kilogram, written as kg, are units used to measure mass. A unit is an agreed quantity used as a standard for measurement.

Volume answers the question of how much space the matter occupies. Litre, written as L, and millilitre, written as mL, are units used to measure liquid volumes. These symbols name units; they are not names of substances.

Consider identical tumblers containing different amounts of water. Water in a half-filled tumbler occupies less space than water in an almost full tumbler. The first sample therefore has a smaller volume, even though both samples consist of the same material.

A balance can be used to compare masses. Observing how much space a sample occupies concerns its volume. Keeping these two ideas separate helps when describing materials: the quantity of matter and the space it occupies are different properties.

How do shape and volume distinguish the three states of matter?

A state of matter is a physical form in which matter exists. The three states considered here are solid, liquid and gas. Shape describes an object's form or outline; volume describes the space it occupies. Both properties help classify a sample.

A solid has a definite shape and a definite volume. A liquid has a definite volume but no definite shape of its own. A gas has neither a definite shape nor a definite volume of its own.

Which examples belong to each state?

Water vapour is water in its gaseous state. Water also exists as solid ice and as liquid water. These forms make a useful comparison because their properties differ even though they are states of the same substance.

An ice cube retains its shape when moved between containers, provided it has not melted. Liquid water changes shape when poured into a differently shaped container. Water vapour spreads into the entire available space. A change of container therefore helps reveal differences between the states.

The shape of a container is not necessarily the shape of each piece of matter inside it. For example, a collection of solid grains can take the overall shape of its container. Each grain remains a solid; this does not make the material a liquid.

Note: Air inside a balloon is the gas being considered. The balloon is the container. Distinguish the material being classified from the object holding it.

How do particles and the spaces between them explain matter?

Matter consists of extremely small constituent particles, meaning the tiny units that make up a larger piece of a substance. These are much smaller than the visible grains obtained by crushing chalk. Even a tiny speck of chalk contains many constituent particles.

The tiny particles making up matter include atoms and molecules. An atom is a basic particle of an element, a substance made of one kind of atom. A molecule is a particle formed by atoms joined together. Detailed atomic structure is not needed to compare the states.

What is interparticle space?

Interparticle space means the space between constituent particles. When the particles being discussed are molecules, this is called intermolecular space. Closely packed particles still have spaces between them. Close packing does not mean that a solid is a continuous material with no gaps.

Sugar added to pebbles enters gaps between the pebbles. Similarly, sand can enter spaces between glass balls. These visible arrangements help illustrate how smaller pieces can occupy spaces between larger pieces. The pebbles and grains themselves still contain extremely small constituent particles.

Dissolving sugar in water gives another way to explore spacing. Dissolving is the process in which a substance spreads through a liquid to form a solution. A solution is a uniform mixture, with its substances evenly distributed throughout.

1. Take a glass vessel about half-filled with water and mark the starting level.
2. Add two teaspoons of sugar and mark the raised level before stirring.
3. Stir with a glass rod until the sugar dissolves, then mark the level again.
4. Compare the level after dissolving with the raised level recorded before stirring.

After dissolution, the level may decrease to some extent. Sugar particles occupy available spaces between water particles. Do not claim that the level must return exactly to the original mark, or that the sugar has ceased to exist because its grains are no longer visible.

How do attraction and motion differ in solids, liquids and gases?

Interparticle attraction is the attractive force between the particles of matter. A force is a push or a pull; attraction draws particles towards one another. The term cohesive force means attraction between particles of the same substance.

The strength of attraction depends on the nature of the substance and the distance between its particles. Particle arrangement, spacing, attraction and movement together explain why different states have different properties. Merely saying that all matter contains particles does not explain those differences.

How are the particles arranged?

Vibration is to-and-fro movement about a position. Solid particles vibrate; they are not motionless. In liquids, particles can move past one another, explaining flow. Negligible means so small that it can be ignored for the explanation being considered.

Generally, particles in a liquid are somewhat farther apart than in the solid state. Ice is an exception: its particles are farther apart than those in liquid water. This exception matters when applying the usual comparison to the different states of water.

Three drawings labelled Solid, Liquid and Gas connect objects to enlarged particle arrangements. The solid has closely ordered circles, the liquid has close but less ordered circles, and the gas has widely separated circles.

See Fig. 7.12 in your NCERT textbook

The circles are a model, a simplified representation used to explain an idea. They show relative arrangements and spaces. They are not photographs of individual atoms or molecules and do not show that gas particles are larger than solid particles.

What observations reveal particle motion?

Particle motion helps explain changes that can be observed even when the particles themselves cannot be seen. A familiar example is the fragrance of a burning incense stick spreading through a room. Particles of the fragrance spread, and moving air particles help them do so.

What happens to tiny particles suspended in air?

Suspended particles are small pieces dispersed in a gas or liquid rather than settled at the bottom. Tiny smoke particles suspended in air are continually hit by invisible gas particles. Their movement provides evidence that the gas particles are moving.

Brownian movement is the irregular, random movement of tiny suspended particles caused by collisions with particles of the surrounding fluid. A fluid is a substance that can flow; both liquids and gases are fluids. A collision means particles striking one another.

Distinguish the smoke particle from the constituent particles striking it. A visible or observable speck of smoke is not a single gas molecule. The larger suspended particle moves because the surrounding particles keep colliding with it.

How does heating affect movement?

When a solid is heated, its particles vibrate more vigorously. The particles have greater movement about their positions before the solid changes state. The particles themselves are not becoming visible merely because the substance is warmer.

In liquids, heating also increases particle movement. With sufficient heating, a liquid can change to vapour. In gases, particles move freely in all directions. These differences connect the particle model to observations of solids retaining shape and fluids flowing.

Use precise language when comparing the states: solid particles vibrate, liquid particles move within a limited space, and gas particles move through the available space. Describing all three simply as “particles that move” misses the difference in the freedom of their movement.

How can observations of containers explain liquid and gas behaviour?

A change of shape does not necessarily mean a change of volume. Liquid water provides a direct demonstration. Take clean, dry containers of different shapes, each with a mark showing a volume of 200 mL, or 200 millilitres.

How can a liquid keep its volume while changing shape?

1. Fill the first container with water to its 200 mL mark.
2. Transfer the water carefully into the second container without spilling it.
3. Observe the new shape of the water and compare its volume with the marked level.
4. Transfer the same water to the third container and repeat the comparison.

The water takes the shape of each container while its volume remains 200 mL. Its particles move past one another but remain close together. This explains how a liquid can have a definite volume without a definite shape of its own.

If a container is not clean, some water may stick to its walls. The next container may then receive slightly less than 200 mL. Such a transfer loss does not show that liquids lack a definite volume.

The drawing shows a bottle labelled A, a jug labelled B and a tumbler labelled C. Each holds water with an arrow marking 200 mL. A, B and C identify the containers.

See Fig. 7.5 in your NCERT textbook

Why is air easier to compress than water?

Compression means reducing the volume occupied by a substance by pressing it. In a syringe without a needle, air trapped behind a blocked opening occupies less space when the plunger, the movable piston inside the syringe, is pushed inward.

The gas particles are pushed closer together, reducing the large spaces between them. Water is practically incompressible in the same comparison. This means that its volume is not appreciably reduced by that pressing action, not that its particles have no spaces between them.

How do melting, freezing and the formation of vapour change a state?

Melting is the conversion of a solid into a liquid. Freezing is the conversion of a liquid into a solid. Heating ice produces liquid water; placing water in a sufficiently cold environment, such as a freezer, produces ice.

Temperature describes how hot or cold something is. The melting point is the minimum temperature at which a solid melts at atmospheric pressure. Atmospheric pressure is the force exerted per unit area by the surrounding air. The condition matters when describing a melting point.

What happens to the particles during melting?

As heating continues, solid particles vibrate more vigorously. They begin leaving their fixed positions as the forces holding them there are overcome. In the resulting liquid, particles can move past one another while remaining close together.

Boiling is rapid vapour formation throughout a liquid, including its interior. The boiling point is the temperature at which a liquid boils and turns into vapour at atmospheric pressure. Vapour bubbles form within the liquid during boiling.

Further heating of liquid water can produce water vapour. Vapourisation means conversion of a liquid into vapour. Its reverse, condensation, is conversion of vapour into liquid. These processes allow water to pass between its liquid and gaseous states.

Three state boxes are joined by arrows in both directions. The left box says Solid, and Melts labels the first forward change. Complete the other state boxes with Liquid and Gas, and the remaining changes with Freezes, Evaporates and Condenses.

See Fig. 8.5 in your NCERT textbook

A physical change changes properties such as shape, size or state without forming a new substance. Ice melting and water freezing are physical changes. Ice, liquid water and water vapour are different states of the same substance.

How do evaporation and condensation occur around us?

Evaporation is the conversion of a liquid into vapour at its surface. It occurs even below the boiling point. Water left on a steel plate can disappear through evaporation, and wet clothes dry as their water changes to vapour.

Evaporation occurs even at room temperature. It does not require the whole liquid to boil. During boiling, vapour forms rapidly both at the surface and within the liquid; evaporation below the boiling point is the slower surface process.

What makes evaporation faster or slower?

Humidity means the amount of water vapour in the air. Clothes dry slowly on a rainy day when humidity is high. Comparing equal amounts of water while changing one condition helps identify its effect on evaporation.

Where do droplets on a cold tumbler come from?

Water vapour in the air can form liquid droplets when it contacts a cold surface. This is condensation. A tumbler containing cold water and ice can therefore acquire droplets on its outer surface.

Droplets outside the tumbler do not by themselves prove that water passed through the glass. Marking the inner water level helps test that suggestion. The water level does not go down while additional water collects outside through condensation.

Note: Water vapour is invisible. What is visible as a cloud of steam contains tiny water droplets. Do not identify the visible droplets as individual gas particles.

Evaporation also causes cooling. Water seeping through an earthen pot evaporates and cools the water inside. Moving air helps sweat evaporate from the body, which explains the cooling associated with sitting under a fan.

How does sublimation differ from melting and evaporation?

Sublimation is the direct conversion of a solid into vapour, below its melting point, without passing through the liquid state. It differs from melting, in which a solid first becomes liquid. It also differs from evaporation, which begins with a liquid.

Camphor provides an example. On heating below its melting point, solid camphor changes directly into vapour. The important observation is the direct change of state, rather than simply the fact that material appears to disappear from the original place.

What is the reverse change?

Deposition is the direct conversion of vapour into a solid without becoming a liquid. Cooling camphor vapour can produce solid camphor again. Sublimation and deposition therefore connect the solid and gaseous states without an intervening liquid stage.

In a mixture of camphor and sand, camphor can sublime while sand remains behind. Solid camphor deposits may be found on a cooler collecting surface. The two materials behave differently on heating, making it possible to separate them.

The process names tell you both the starting and finishing states. To distinguish them, first identify what was present before the change, then identify what formed afterwards. A substance becoming less visible is not enough information to decide whether evaporation or sublimation occurred.

Do not force every change of state into a solid-to-liquid-to-gas sequence. The direct route between solid and vapour is the feature that distinguishes sublimation and deposition from the changes involving liquid water.

How do heating and cooling change the size of matter?

Expansion is an increase in size or volume; contraction is a decrease. Heating can produce expansion, while cooling can produce contraction. These changes need to be distinguished from a change of state: a substance can expand while remaining in the same state.

How can expansion of a solid be demonstrated?

A ball and ring apparatus consists of a metal ball and a metal ring selected so that the cool ball passes through the ring. When the ball alone is heated, it expands and no longer passes through the unheated ring.

After the ball cools, it contracts and can pass through the ring again. The change in whether the ball fits shows a change in its size. The ball remains solid during this demonstration; expansion does not mean that it has melted.

How can expansion of liquids and gases be demonstrated?

A capillary tube is a tube with a very narrow bore, meaning a narrow internal passage. In a liquid-expansion demonstration, a test tube is filled to the brim with water and fitted with a cork carrying a capillary tube.

On heating, the water rises into the capillary. The narrow passage makes the change in level easy to observe. The rising level demonstrates expansion of the heated liquid, rather than the formation of more water.

For the gas demonstration, a test tube containing air is fitted with a cork and capillary. Some coloured water is placed in the capillary. On heating the test tube, the coloured water rises as the enclosed air expands.

Note: An apparently empty test tube contains air. In the gas-expansion demonstration, the coloured water shows the effect of the expanding air; it is not the gas being studied.

Read each demonstration by identifying the material heated and the observed change. The metal ball changes size, the water level rises in the liquid experiment, and expanding air moves the coloured water in the gas experiment. These are qualitative observations, not measurements of equal expansion.

How can heating cause both physical and chemical changes?

A chemical change forms one or more new substances. Heating can cause a physical change, such as melting, or help bring about a chemical change, such as burning. The deciding question is whether a new substance has formed.

A candle demonstrates both kinds of change. Its wax melts near the flame, moves up the wick, the thread that carries liquid wax, and evaporates. Wax vapour then burns. Melting and burning must therefore be described as different parts of the process.

Which candle changes are physical?

1. Solid wax near the flame becomes liquid wax through melting.
2. The liquid wax is carried up the wick towards the flame.
3. Wax evaporates because of the heat of the flame, forming vapour.
4. Liquid wax that cools can become solid again through solidification, the change from liquid to solid.

Melting, evaporation and solidification are physical changes. They change the state of the wax. The movement of liquid wax up the wick is part of the sequence leading to the supply of vapour to the flame.

Why is burning wax a chemical change?

Combustion is a chemical reaction in which a substance reacts with oxygen and produces heat and/or light. A chemical reaction is a process that forms new substances. Oxygen is the component of air that supports combustion.

Wax vapour burns and produces new substances, including carbon dioxide, a gas formed here from carbon in the wax and oxygen in the air. This formation of a new substance makes burning a chemical change.

A physical change is not defined simply as a change that can be reversed. Crushing chalk changes its size without forming a new substance, even though the original chalk piece is not recovered by simply reversing the crushing action.

Glossary

• Matter — Anything that has mass and occupies space, including solids, liquids and gases.
• Mass — The quantity of matter in an object, measured using units such as grams and kilograms.
• Volume — The space occupied by matter, measured for liquids using units such as litres and millilitres.
• Constituent particle — A tiny basic unit making up a larger piece of a substance or material.
• Interparticle space — The space between constituent particles, which differs across the states of matter.
• Cohesive force — The attractive force acting between particles of the same substance.
• Brownian movement — Irregular movement of tiny suspended particles caused by collisions with surrounding fluid particles.
• Melting — The change of a substance from its solid state into its liquid state.
• Freezing — The change of a substance from its liquid state into its solid state.
• Evaporation — Conversion of a liquid into vapour at its surface, occurring even below its boiling point.
• Condensation — The conversion of vapour into liquid, as when water droplets form on a cold surface.
• Sublimation — Direct conversion of a solid into vapour below its melting point, without becoming liquid.
• Expansion — An increase in the size or volume of matter, demonstrated when suitable samples are heated.
• Physical change — A change in physical properties, such as shape, size or state, without forming a new substance.
• Chemical change — A change in which one or more new substances are formed through a chemical reaction.

Common errors and misconceptions

• Misconception: Liquids have neither a definite shape nor a definite volume. Correct: Liquids have a definite volume but take the shape of their container. Gases have neither a definite shape nor a definite volume of their own.
• Misconception: Particles in a solid do not move. Correct: They vibrate about fixed positions. They do not move past one another as particles in a liquid do.
• Misconception: Dissolved sugar has disappeared from existence. Correct: Sugar particles remain in the solution and occupy available spaces between water particles, although individual sugar grains are no longer visible.
• Misconception: Evaporation requires boiling. Correct: Water evaporates even at room temperature. Evaporation below the boiling point occurs at the surface, while boiling involves rapid vapour formation within the liquid as well.
• Misconception: Visible steam is made of visible water-vapour particles. Correct: Water vapour is invisible. Tiny liquid droplets make the cloud associated with steam visible.
• Misconception: Sublimation means solid turning into liquid. Correct: That change is melting. Sublimation goes directly from solid to vapour without passing through the liquid state.
• Misconception: All changes in a burning candle are chemical. Correct: Melting, evaporation and solidification of wax are physical changes; the burning of wax vapour is a chemical change.
• Misconception: Every physical change can easily be reversed. Correct: Physical changes are identified by the absence of new substances. Crushing chalk remains a physical change even when its original form is not readily restored.

Exam-style questions with model answers

Q1. Define matter and volume. [2 marks]

1. Matter is anything that has mass and occupies space.
2. Volume is the space occupied by matter; for example, liquid water occupies a measurable space in its container.

Q2. Compare solids, liquids and gases using both shape and volume for each state. [3 marks]

1. A solid has a definite shape and a definite volume. Moving it to another container does not make it take that container's shape.
2. A liquid has a definite volume but no definite shape of its own. It takes the shape of its container.
3. A gas has neither a definite shape nor a definite volume of its own. It spreads through the available space.

Q3. Water of volume 200 mL is transferred without spilling from a clean, dry bottle to a clean, dry jug, then to a clean, dry tumbler. No water is lost during transfer. State the final volume and explain the changes in shape and particle movement. Give three points. [3 marks]

1. The final volume is 200 mL because the same water is transferred without loss. A liquid has a definite volume under these conditions.
2. The water takes the shape of the jug and then the tumbler. It has no fixed shape of its own.
3. Water particles can move past one another while remaining close together. This allows the liquid to change shape while retaining its volume.

Q4. Water is heated from ice to liquid and then to vapour. The vapour is cooled to liquid, which is then frozen. Name each of these four changes and identify its starting and finishing states. [4 marks]

1. Ice changing into liquid water is melting. The starting state is solid and the finishing state is liquid.
2. Liquid water changing into water vapour is vapourisation. The starting state is liquid and the finishing state is gas.
3. Water vapour changing into liquid water is condensation. The starting state is gas and the finishing state is liquid.
4. Liquid water changing back into ice is freezing. The starting state is liquid and the finishing state is solid.

Q5. A cool metal ball passes through an unheated metal ring. After only the ball is heated, it cannot pass through; after cooling, it passes through again. The ball remains solid and no new substance forms. Explain the observations and classify the change in five points. [5 marks]

1. Initially, the cool ball is small enough to pass through the ring. This gives the starting observation against which the heated ball can be compared.
2. Heating the ball causes expansion, which means an increase in its size. The ring has been left unheated during this comparison.
3. The expanded ball no longer passes through the opening. The changed fit provides evidence that heating has changed the ball's size.
4. Cooling causes contraction, meaning a decrease in size. The cooled ball can therefore pass through the same ring again.
5. This is a physical change because no new substance forms. It is expansion and contraction rather than melting, since the ball remains solid.

Q6. At a burning candle, solid wax melts, liquid wax moves up the wick, wax evaporates, and its vapour burns to form new substances. Some melted wax cools into a solid. Explain these five stages and identify the physical state changes and the chemical change. [5 marks]

1. Solid wax near the flame melts into liquid wax. This is a physical change because the wax changes state without forming a new substance.
2. Liquid wax moves up the wick, the thread carrying it towards the flame. This supplies wax to the region where vapour can form.
3. The heated liquid wax evaporates into vapour. This is another physical change because it is a change from liquid to gas.
4. Wax vapour burns, producing new substances. Burning is therefore the chemical change in the sequence, rather than simply another change of state.
5. Melted wax that cools becomes solid through solidification. This is a physical change from liquid to solid; the material is still wax.

Q7. A glass vessel contains water with its level marked. Sugar is added, raising the level; after stirring, the sugar dissolves and the raised level decreases to some extent. Explain the observations using particles in three points. [3 marks]

1. Sugar separates into extremely small constituent particles as it dissolves. The original visible grains are no longer seen in the liquid.
2. The sugar particles occupy available spaces between water particles. This helps explain the decrease from the raised level observed before stirring.
3. The sugar remains present in the solution. The stated decrease does not establish that the liquid must return exactly to its original water-level mark.

Q8. Camphor is heated below its melting point and changes directly from solid to vapour. On a cooler surface, its vapour changes directly back into solid camphor. Name and define both changes. [2 marks]

1. The first change is sublimation: solid camphor changes directly into vapour without becoming liquid.
2. The second is deposition: camphor vapour changes directly into solid without passing through the liquid state.

Key takeaways

• Matter has mass and occupies space. Mass describes the quantity of matter, while volume describes the space it occupies.
• Solids have definite shape and volume; liquids have definite volume; gases have neither a definite shape nor a definite volume.
• Matter contains tiny particles with spaces between them. Differences in attraction and movement explain differences between the states.
• Solid particles vibrate about fixed positions. Liquid particles move past one another, while gas particles move freely through available space.
• Melting, freezing, evaporation and condensation change physical state. Sublimation changes a solid directly into vapour without an intervening liquid stage.
• Evaporation occurs even below the boiling point. Water vapour is invisible, while condensed droplets can make steam appear visible.
• Heating can cause expansion, a change of state or a chemical change. Identify the actual observation before naming the process.
• A burning candle involves physical changes of wax and a chemical change when wax vapour burns to form new substances.

Test yourself

What two properties must something have to be matter?

It must have mass and occupy space. The space occupied is its volume.

Why can a liquid change its shape without losing its definite volume?

Its particles can move past one another while remaining close together within a limited space.

Are the constituent particles of a solid motionless?

No. They vibrate about fixed positions rather than moving freely past one another.

Why is air in a blocked syringe compressible?

Its particles have large spaces between them. Pressing the plunger pushes the particles closer together.

What is the difference between evaporation and condensation?

Evaporation changes liquid into vapour at its surface; condensation changes vapour back into liquid.

What distinguishes sublimation from melting?

Sublimation changes solid directly into vapour, while melting changes solid into liquid.

Why does water rise in the capillary of the liquid-expansion demonstration?

The heated water expands and occupies more space, making its level rise in the narrow tube.

Why is melting wax a physical change but burning wax vapour a chemical change?

Melting changes the state of wax without forming a new substance. Burning produces new substances.