Majority of things that we see around us are said to be examples of matter. What is matter? Can you name some things that are matter around you. The whole concept of matter was coined at around 400 BC by Greek Philosophers Democritus and Aristotle.
to Democritus, if you cut matter into smaller
and smaller pieces, you end up with its smallest bits which
cannot be cut further. He called these ‘atomos’ which there
after came to be known as ‘atoms’.
Aristotle, at around 350 BC, modified
the Democritus theory to state that matter was made up of four elements namely: fire, earth, air and water.
His theory persisted for about 2000 years and was later
dismissed and replaced by the modern day atomic theory proposed by English Scientist John Dalton. Atomic theory was as a result of experimentation into the nature of matter. It paved the way for
deeper understanding of what happens during chemical reactions. This unit is about the various states of matter. So then, what is matter? What are the various states of matter? What happens when various forms of matter are subjected to different conditions?
After studying this unit, I should be able to relate properties of matter to daily life physical and chemical phenomena.
3.1 Definition of matter
3.2 Changes of states of matter
3.3 Physical and chemical changes
3.4 Kinetic theory of matter
3.1 Definition of matter and the states of matter
1. Look around you, inside and outside your class.
2. Name some of the objects you can see, smell or touch. Classify them into those that occupy volume and those that have weight.
3. How can you know that an object occupies volume and has weight?
4. Add more water to a glass that is already full of water. What happens?
Objects such as books, pens, trees, water, animals, stones and soil can be seen and felt. All these objects occupy volume and have weight.
If an object is heavy, then it has weight. you add more water to a glass full of water. The excess water spills
over. Water occupie volume.
All the objects mentioned in the discussion corner that have mass and occupy volume are made up of some materials.
All substances that are found in nature are made up of matter. Matter is anything that occupies volume and has mass.
Matter can be put into three different groups, that is:
• Solids - for example soil, chalk, salt, sugar, wood and metals.
• Liquids - for example water, kerosene, milk and spirit.
• Gases - for example air, biogas, oxygen and carbon dioxide.
These three groups are commonly known as states of matter. Each of these states of matter has characteristic properties.
following table gives characteristic properties of the three states of matter.
Table 3.1 Properties of the three states of matter
1. Name the three states of matter.
2. Classify each of these items into the three states of matter: Books, ozone, air,milk, water, trees, salt and chalk.
3. (a) What are some of the things around you that are not matter?
(b) Why do you think
they are not considered to be matter?
3.2 Changes of states of matter
1. (a) What can you conclude when you wake up and find a lot of water droplets on grass yet it was hot and dry the previous day?
(b) Does this water remain on the grass the whole day?
2. (a) What happens to a candle as it burns?
(b) What causes
the change in 2 (a) above?
(c) Can the burnt candle be remoulded?
3. What happens when wood is burnt in limited supply of air?
Water droplets on grass are formed due to convertion of water vapour in the atmosphere into moisture. In the course of the day as temperature increases, the moisture again turns into vapour.
If you light a candle, it gives out light as it changes to
liquid form. After this change, the melted wax can still be used to make a new candle. This is called remoulding.
When wood is burnt in limited air supply, charcoal is produced.
Matter can be converted from one state to another.
Reagents and apparatus
Bunsen burner, cooking fat, piece of ice, matchbox, glass beaker.
Caution! Remember the correct procedure of lighting the Bunsen burner to avoid
accidents in the laboratory.
Put off Bunsen burner after heating to save gas. Also use the cooking fat sparingly.
1. Put some cooking fat in a beaker.
2. Place the beaker over a non-luminous flame. Observe what happens to the fat.
Question: How would you produce a non-luminous flame from a Bunsen burner?
3. Take the melted fat and place it in cold water. Note the changes.
4. Repeat procedures 1 and 2 with a piece of ice and note down your
1. At what temperature does the cooking fat change its state?
2. Explain what happens to the fat when placed in cold water.
3. What happens to ice when placed over the flame?
When the cooking fat is heated, it changes into liquid form. This also happens when ice is heated. When placed in cold water, the liquid fat changes back to solid.
When some solids are heated they change into liquids. This process is called melting. When the liquids are cooled they change back into the solid state. This process is known as freezing.
When a piece of ice is heated, it changes into
liquid water. The water slowly changes into vapour with continued heating. The process through which water changes state from liquid to gas is known as evaporation. When the vapour is cooled, it changes
back into liquid form. This process
is called condensation. It is also possible to change a solid directly into a gas. This is called sublimation. However, when a gas changes directly to a solid; the process is called deposition.
3.3 Physical and chemical changes of matter
There are two types of changes that matter can undergo; namely:
• Physical change
• Chemical change
In activity 3.2, when the cooking fat and the piece of ice are heated, no new substances are formed. The processes are also reversible.
Such changes are known as physical changes. A physical change is also known as a temporary change.
Some changes lead to the formation of new products. Such changes are irreversible.
They are referred to as chemical changes. A chemical
change is also referred to as a permanent change.
(a) Physical Changes
Experiments demonstrating physical changes
Investigating changes that occur when ice is heated
Apparatus and reagents
Ice, thermometer, beakers, Bunsen burner
and tripod stand, wire gauze
1. Half-fill a beaker with some ice.
2. Put in the thermometer carefully
immediately into the ice and record the
rise in temperature.
3. Arrange the apparatus as in figure 3.6
(The teacher will demonstrate how to
arrange the apparatus then one member
of your group will guide the other
members) and heat the ice gently while
with the thermometer.
Record your observations.
Fairness is my other name!
Ensure you record accurate readings obtained from your thermometer. Never use other people’s readings or use guess work. Be honest!
4. Record the temperature of the ice
every 30 seconds in the table provided until all the ice melts. Continue heating while recording the temperature until boiling occurs.
5. (a) After boiling, continue heating for about two minutes. Record your results in a table like the one shown below.
(b) Plot a graph of temperature (vertical axis) against time (horizontal axis).
1. (a) What does ice form when it melts?
(b) Did temperature change during melting?
(c) Give a reason for your answer in 2(b) above.
2. (a) What does water change to when it boils?
(b) Did temperature change
(c) Give a reason for your answer in 3(b) above.
3. Why is the thermometer used in this experiment?
When ice is heated, its temperature rises steadily until it reaches 0°C. At this point, ice changes into liquid water.
The temperature remains constant at this point as ice changes to liquid water despite the fact that heating continues. This
process is called melting.
On further heating, the temperature rises steadily up to 100°C when the liquid water starts to change to vapour.
Again the temperature remains constant as the water changes to vapour. The process of a liquid
changing into vapour is called evaporation.
Thermometer in this experiment enables us to know the temperature at which change of
The graph below shows heating of ice until boiling starts.
We can explain what happens in each region as follows:
• Region AB: The temperature rises steadily as the ice absorbs heat energy. The temperature rise stops at 0ºC.
• Region BC: The temperature remains constant (0ºC), until all the
ice has melted. This is because the heat energy absorbed in this region is used to break the forces of attraction holding the solid particles together. Water changes its physical state from solid to liquid form at this point.
• Region CD: Temperature rises steadily as the liquid water absorbs heat energy. The temperature rise stops when the liquid water starts changing into vapour (evaporation).
• Region DE: The temperature remains constant as the liquid water changes
water vapour. Heat energy absorbed is used to break the forces of
attraction holding water particles together. Water thus changes into vapour.
Changes that occur when ice is heated can be illustrated in the following flow
The changes of state from solid to liquid and liquid to gas can be reversed by cooling. On cooling, the gas condenses into liquid and finally the liquid freezes into solid as shown in the flow diagram.
Investigating melting and sublimation
Apparatus and reagents
Candles, iodine, naphthalene, boiling tubes, water, spatula, a pair of tongs, electronic weighing balance, a jar and Bunsen burner
1. Light a candle. Let the candle burn and record your observations.
2. Place a few iodine flakes in a boiling tube and hold the boiling tube with a pair of tongs.
3. Heat the boiling tube gently over a non-luminous flame. Observe and record any observable changes.
Quality is my choice!
Use a weighing balance that has been approved by the Rwanda Standards Board (RSB).
4. Place 5 g of naphthalene in a boiling tube and hold the tube with a pair of tongs or clamp
5. Heat as you observe the changes.
1. (i) What observations are made when the candle is lit?
(ii) State the changes of state that take place when the candle is lit.
2. What is observed when:
(i) Iodine flakes are heated?
(ii) The product obtained is allowed to cool?
is observed when:
(a) Naphthalene is heated
(b) The product is left to cool?
When the candle is lit, it burns with a luminous flame. The candle wax melts into liquid.
When it flows down and cools, it solidifies. The candle wax changes from solid to liquid and from liquid back to solid.
When iodine flakes are heated, they form a purple vapour. The vapour solidifies on the cooler parts of the boiling tube to form a sublimate of pure iodine. The iodine changes directly from solid to vapour. On cooling, the vapour turns back to solid without undergoing the liquid state.
When some solids such as iodine are heated, they change from solid directly to gas without passing through the liquid state. This change is called sublimation.
On cooling, the substances condense from gas to solid. The process is known
Another example of a substance that sublimes is ammonium chloride.
Investigating physical changes
Apparatus and reagents
Test tubes, Bunsen burner, test tube holder, candle wax, water, wooden splints,
zinc (II) oxide, lead (II) oxide, beakers and boiling tube.
1. Place few pieces of candle wax in a test tube.
Hold the test tube with the tube holder and heat.
3. Allow it to cool then record the observations.
4. Heat 5 cm3 of water in a test tube until it boils. Observe the steam formed at the cooler part of the test tube. Record your observations.
5. Take a piece of wooden splint, break it into small pieces. Is there a new substance that is formed?
Place a spatulaful of zinc (II) oxide and lead (II) oxide in two separate test tubes.
7. Hold each with a test tube holder and heat.
8. Allow them to cool and observe their colours when cold.
9. Record your observations.
1. State the observations made when:
(i) Candle wax is heated then allowed to cool.
(ii) Liquid water is boiling.
2. Is there a new substance that is formed when a piece of wooden splint is broken down?
3. Compare the changes that take place
when zinc oxide and lead (II)
oxide are heated separately.
When wax is heated, it melts. On cooling, it solidifies to form the solid wax again. When liquid water is heated strongly, it boils to form steam. When the steam is cooled, it condenses to form liquid water again.
When a piece of wooden splint is broken into small pieces, it does not change to a new substance. Only the shape changes. When zinc oxide is heated, it turns into a yellow powder. On cooling, it turns back to a white powder. All these changes are reversible. Thus the initial substances are obtained on cooling. All these changes are known as physical changes.
As seen from this activity, some of the characteristics of a physical change are:
1. No new substance is formed.
2. The mass of the substance does not change.
3. It is easily reversible.
Cooking fat should always be kept in a cool and dry place to prevent it from melting out.
Investigating chemical changes
Apparatus and reagents
Test tubes, Bunsen burner, wooden splint, a piece of paper, magnesium ribbon, iron nails, water, pair of tongs.
1. Light a wooden splint in a Bunsen burner flame.
2. Allow it to burn
for some time.
3. Compare the product formed with the initial splint. Are they the same?
4. Burn a piece of paper to form ash.
5. Compare the product with the initial paper. It is possible to get back the paper from the ash?
6. Using the pair of tongs, heat a piece of magnesium ribbon on a Bunsen burner flame. Allow the magnesium to burn.
Caution! Burning magnesium
produces intense light that can cause
temporary loss of sight. Do not look directly at the light source.
7. Collect the product and compare it to the initial magnesium ribbon.
8. Place few iron nails in a test tube containing water.
Keep it in an open place for one week. What do you observe?
10. Explain your observation in (9) above.
1. (a) State the observations made when the following substances are burnt.
(i) Wooden splint (ii) Piece of paper (iii) Magnesium ribbon
(b) How are the products formed in (a) above different from with the initial substances?
(c) Are there new
substances that are formed?
(d) Why are those changes considered to be chemical changes?
2. Explain what happens when iron nails rust.
When a wooden splint and paper are burnt, they form ash. The properties of ash are different from those of wood and paper. It is not possible to convert ash back into wooden splint or paper. Ash is a completely new substance. Thus the initial substances
obtained on cooling. When magnesium is burnt in air, it produces a brilliant white flame and ash. Energy is given out in form of heat and light.
After one week, a red brown coating forms on the nails.
Rusting is a process by in
which iron combines with oxygen and moisture to form rust.
Rust is a red-brown solid. It is impossible to convert rusted nails back to the clean ones.
It is advisable to paint iron sheets to avoid regular expenses of replacing them when they rust.
When wood is burnt, it changes to ash. We cannot get back wood from the ash.
This reaction is thus irreversible. Similarly, when magnesium is burnt in air, it forms powder. It is not possible also to get back the magnesium ribon from the powder. The
white powder formed is called magnesium oxide. It is as a result of combining magnesium with oxygen in air.
All these processes are well reversible. They are therefore called permanent changes. Parmanent changes are chemical changes.
of the characteristics of chemical changes include:
1. New substances are formed.
2. It is difficult to change the new substance back into the original substance.
1. Cooking fat should be stored in a cool dry place. What is the importance of this precaution?
2. State whether the following are physical or chemical changes.
(i) Burning a match stick into ash.
(ii) Freezing water to make an ice cube.
Explosion of a bomb.
3. (i) Zinc oxide changes to _____________colour on heating and
________________________colour on cooling. It undergoes a__________
(ii) Iodine changes to _________________________ on heating and
cooling. It undergoes _______________
4. State whether the following statements are true or false.
(a) Burning wood is a chemical change.
(b) Drying a shirt in the sun is a chemical change.
(c) Dissolving sugar in tea is a physical
(d) Cooking meat is a chemical change.
3.4 Kinetic theory of matter
To investigate the movement of particles.
1. Get some marbles and a plastic bottle with a cap.
2. Put a few marbles for example 5 in the bottle then close the cap.
3. Agitate the marbles by shaking the bottle. What do you observe?
Fill the bottle half way with marbles and shake the bottle once more.
5. Compare how the marbles move with the first instance.
6. Now, fill the bottle completely with marbles, close the cap and try shaking the bottle. Do the marbles move?
7. Explain your observation in (6) above.
8. Compare the three scenarios to the arrangement of particles in solids, liquids and gases.
9. Discuss the results of the experiment in your group and write a summary report.
The fewer the marbles are in the bottle, the more they move when the bottle is shaken. When the bottle is full, the marbles hardly move.
Matter consists of particles arranged in a certain way. This arrangement varies from one state of matter to another.The arrangement and movement of particles in solids, liquids and gases is explained by the Kinetic theory of matter. The word kinetic is
derived from the Greek word ‘Kineo’ which implies ‘motion’.
The kinetic theory therefore explains:
• how particles that make up matter are packed in solids, liquids and gases
• the movement of these particles.
• the attractive forces between
the particles and the effect of temperature on them.
According to the Kinetic theory, particles in matter are always in constant motion.
For this reason, they posses kinetic energy. Kinetic theory of matter can be used to explain the
properties of the various states of matter. The theory also explains
what happens during change of state.
Packing of particles in terms of kinetic theory
Particles of a solid are closely packed. They are held in fixed positions by
strong interparticle forces of attraction. They therefore vibrate but they do not move from one place to another. It is for this reason that solids have a fixed shape.
In a liquid, particles are free to move randomly but tend to stick together.
This is because they have moderate forces of attraction between them. They are hence less closely packed as compared to solid particles.
The particles of a gas have weaker forces of attraction between them. This is why they are very far apart.
They are therefore free to move randomly in any direction.
For this reason, a gas occupies the entire space of a container and so a gas has no definite shape.
3.5 Change of state and kinetic theory
In pairs discuss the following.
1. What can you do to convert solid ice to water?
2. What is required for one to convert water into steam?
3. Give the names of the processes that take place in (1) and (2) above?
4. What is done to reverse
the processes you have mentioned in (3) above?
5. Give the names of the reverse processes by which steam is converted to water and water to soild ice?
The conversion of soild ice to water involves heating and the process is called melting. Conversion of water to ice also involves heating and is called evaporation.
However, reversing these two processes requires cooling. The process by which steam
is converted to water is called condensation while the conversion of water is solid ice is called freezing.
The various processes that lead to change of state include:
When a solid is heated, the kinetic energy of the particles increases and they vibrate more vigorously
within their fixed positions. Further heating weakens the forces of attraction between the particles. The solid thus changes to liquid. This is the melting process. The temperature at which melting occurs is known as the melting point.
a liquid is heated the particles gain more kinetic energy and the particles
start to move more rapidly. When the liquid gets hot enough
the forces of attraction joining the fast moving particles at the surface are broken detaching them from the other particles. The surface particles thus escape into the air. This process is known as evaporation.
The liquid then changes into gaseous state. The temperature at which evaporation takes place is called the boiling point.
When the gas is cooled, the kinetic energy of its particles decreases. The movement of the particles
slows down and they come close together. At this point the attractive forces between the particles become sufficient to hold them together. The gas then becomes a liquid. This process is called condensation.
in temperature, makes the liquid particles to slow down their movement further. The particles come closer together and the forces of attraction between them increase. They hence vibrate within fixed positions. The particles are not free to move from
one place to another. A solid is hence formed. This process is called freezing.
1. What name do we give to the following processes:
a) Change of solids to liquids
b) Change of liquids to solids.
2. Draw a diagrammatic representation of the arrangement of particles in solids, liquids and gases.
3. The following graph shows
the changes that occur when a solid is heated until boiling starts. Study it and answer the question that follow.
Explain what happens in regions:
(i) P Q (ii) Q R (iii) R S (iv) S T
4. State whether the changes that occur after the following activities are physical or chemical changes. Give a reason for each case.
(i) Place unripe bananas in a paper bag
and keep them for 10 days. Observe the changes on the tenth day. Compare the unripe banana with the product you get after 10 days.
(iii) Place some glucose in warm water and add 3 g of yeast. Leave the
mixture in a warm place (30ºC) for three
days. Comment on the smell
produced by the product.
On June 13 2015, at least five people died and 100 others were hospitalised in an area in the Northern Indian state of Punjab. Several residents of the area complained of breathing problems.
This was after a tanker carrying ammonia gas got stuck under
a bridge resulting in the gas leak. What do you think happened to the residents?
The residents might have been admitted in hospitals because they inhaled the gas which was poisonous.
Ammonia is one of the most poisonous gases known. It is lighter than air. It can hence move easily from one place to another. It is colourless. Ammonia has a pungent suffocating odour.
1. (a) Do you have compost pits in your school?
(b) If you have them, where in the school compound are they located?
(c) Why do you think they are dug in such locations?
2. Why do you think latrines are always built considering the direction
of wind and a distance away from the main house?
Compost pits and latrines should be built a distance away from the houses because of the smell. This is to prevent discomfort to the house residents.
The main house and the latrine should be built in parallel to the usual direction of wind.
Inhalation of poisonous gases and irritating smell occurs due to movement of gas particles from one place to another.
Movement of particles of a substance from a region of high concentration to a region of low concentration is called diffusion.
a) Investigating diffusion
Apparatus and reagents
A beaker of water, a container of ink, a can of perfume spray.
1. (a) Add a drop of ink into the water. What do you notice?
(b) Add another drop of ink. Does
the same thing happen again?
(c) What do you conclude?
2. Remove the lid of the perfume can and press on top away from everyone. What do you notice after a few minutes?
Let the students who are perfume intolerant stay away from the perfume.
When a drop of ink is placed onto a beaker of water, the ink particles spread until all the water is uniformly coloured. Also, after a few minutes of opening the perfume can, the smell of the perfume can be felt in the air.
The ink spreads in water
and perfume is smelt due to the movement of particles from ink into the water and those of perfume into the air. We can hence say that the particles moved from the region where they were great in number to the region where they are fewer in number
by the process of diffusion.
b)Investigating diffusion in gases
Apparatus and reagents
Long glass tube, concentrated ammonia solution, concentrated hydrochloric acid, cotton wool, tongs, clamp stand.
1. Clamp a long glass tube horizontally as shown in figure 3.12
2. Sock two pieces of cotton wool, one piece in concentrated ammonia solution and the other in concentrated hydrochloric acid separately (do not allow the soaked pieces
to come close to one another).
Caution! Ammonia and hydrogen chloride gases are poisonous. Always waft gas towards your nose if you have to smell them.
3. Quickly insert the soaked cotton wool pieces simultaneously at the opposite ends
of the long glass tube.
4. Carefully observe what happens in the glass tube.
5. Measure the distance from both ends of the glass tube to the position where a patch is seen.
1. What observations are made in the glass tube?
2. At what distance from both ends of the long glass tube are the observations made?
3. Explain the observations made in the tube.
The cotton wool soaked in concentrated ammonia solution gives out ammonia gas whereas the cotton wool soaked in concentrated hydrochloric acid gives out hydrogen chloride gas. Ammonia and hydrogen chloride gases diffuse in the long glass tube. When the two gases meet, they react to form dense white fumes of ammonium chloride after about 5 minutes. The ammonium chloride is seen as a white ring.
The white ring is formed closer to the end with cotton wool soaked in concentrated hydrochloric acid. Ammonia gas has less dense particles. Its particles therefore, moves faster than hydrogen chloride gas particles.
Diffusion is affected by several factors namely; temperature, concentration gradient, surface area and density of the particles. Diffusion occurs faster at higher temperatures than at lower temperatures. A gas with low density diffuses faster than
with high density. Diffusion does not take place in solids.
1. What would happen if you hit a heap of marbles with a single marble from above?
2. What about if you placed marbles in a closed container and shook the container?
3. In either case, what kind of motion will the marbles make?
When a heap of marbles are hit from above, they scatter in all directions. Again when the container having marbles is shaken, the marbles move about hitting all sides of the container.
Brownian motion is the random movement of particles suspended in a fluid. This is as a result of the movement of the particles from their collision with the quick moving particles in the fluid.
This phenomenon is named after Robert Brown an English
Botanist who discovered it. In 1827, while examining grains of pollen of a plant suspended in water under a microscope, Brown observed minute particles ejected from the pollen grains executing a continuous zigzag motion. This kind of movement is what
is known as Brownian motion.
1. You are provided with the following: potassium permanganate, glass tube, beaker,spatula and water. Explain how you would demonstrate diffusion.
2. Just like animals, plants also need certain ions to be able to grow. Explain how they obtain these
ions from the soil.
3. State whether this statement is true or false:
Diffusion is slower in air than it is in liquids.
4. Explain your answer in (3) above.
5. A senior one student placed 200 cm3 of water in a 500 cm3 glass beaker. She
then crushed a piece of chalk into fine powder and placed them in the water.
She stirred and heated the water to boiling as she observed. What was she trying to find out?
• Matter is anything that occupies volume and has mass.
• The three states of matter are: gas, liquid and solid.
• Matter can undergo physical or chemical change.
• Melting is the process by which a solid is converted to a liquid at constant
temperature. The reverse of melting is freezing.
• Vaporisation is the process by which a liquid changes to vapour. The reverse of vaporisation is condensation.
• A physical change is one where no new substance is formed while a chemical change
is when a new substance is formed.
• Kinetic theory of matter states that matter is composed of many small particles that are in constant motion.
• Brownian motion is the random movement of particles suspended in a fluid.
1. State whether the following statements are true or false.
(a) The particles of a liquid are attracted to one another, but cannot move past each other.
(b) The atoms of a solid are very far apart and vibrate in fixed positions.
a gas completely stops all of its particles from motion.
(d) Air has mass.
2. When a thermometer is placed in warm water, the mercury inside moves up.
This is mainly because ____________.
A. the mercury is thin.
B. the particles of
mercury move faster and get a little further apart
C. hot mercury is lighter
D. the glass of the thermometer gets hot.
3. The following figure shows a metal ball and a ring specially made so that at room temperature the ball just fits through
the ring. However, when the ball is heated, it gets stuck and cannot fit through anymore. It gets a little bigger.
Explain how the motion and attractions of the atoms in the metal ball cause it to get slightly larger when heated.
4. Food colouring spreads out faster in hot water than it does in cold water. This is mainly because_____________.
A. the water molecules
in hot water move more quickly.
B. the molecules in hot water are larger.
C. the food colouring molecules are small.
D. hot water is less dense.
5. To describe a gas, you would say_____________.
A. the particles are very attracted to
B. the particles are not very attracted to each other.
C. the particles are very close together like a liquid.
D. the particles of a gas are farther apart than the particles in a liquid or solid.
6. Sometimes, especially on
hot days, a wooden door, that opens and closes easily during cooler months, will be hard to open and close. Why is the door hard to open and close on hot days?