4.3.2 Isotopes

4.3.2 Isotopes

Isotopes are atoms of certain elements which have the same number of protons but different number of neutrons in the nucleus of the atoms.

Isotopes of the same element have same chemical properties. For example, both carbon-12 and carbon-13 burn in oxygen to form carbon dioxide.
3. Physical properties of isotopes are different. For example, carbon-14 isotope has a melting point, boiling point and density that are higher than those of carbon-12 and carbon-13.

Examples of isotopes

4.3 Proton Number and Nucleon Number in Atoms of Elements

4.3 Proton Number and Nucleon Number in Atoms of Elements

4.3.1 Proton Number and Nucleon Number
1. The proton number represents the number of proton found in nucleus of an atom. Sometime, it is also known as the atomic number.
2. Nucleons are the subatomic particles inside the nucleus of an atom,
Nucleon = protons and neutrons
3. Nucleon number represents the number of nucleons in an atom.
Nucleon Number = Number of protons + Number of neutrons

4. In a neutral atom contains an equal number of protons and electrons.
5. Atoms of certain elements can be represented by the following symbol:

  Number of protons = 8
  Number of electrons = 8
  Number of neutrons = 16 – 8 = 8

6. Table below shows the proton number and nucleon number for some elements.
Amount of
Amount of
Amount of
 Relationship between the number of subatomic particles, proton number and nucleon number

4.2 Structure of Atoms

4.2 Structure of Atoms

1. All matter consists of tiny units called atoms.
2. Atom is a basic unit of all matter.

4.2.1 Subatomic Particles
1. An atom is made up of particles that are even smaller called subatomic particles.
 There are three types of subatomic particles, which are
 (a)  Protons
 (b)  Neutrons
 (c)  Electrons

Subatomic particles in an atom

4.2.2 Comparison between Subatomic Particles

Atoms of any element are neutral because the number of protons and the number of electrons in an atom are the same.
2. In a neutral atom, the number of protons is the same as the number of electrons.

4.1.c Changes of State of Matter and Energy

Change in Heat and Kinetic Energy of Particles

1. The change in temperature will influences the kinetic energy or the speed of the motion of the particles.

2. When a substance is heated, the kinetic energy of the particles in the substance increases. This causes the particles to move or vibrate faster.

3. Likewise, when a substance is cooled, the kinetic energy of the particles in the substance decreases. This causes the particles to move or vibrate slower.

4. The kinetic energy of the particles in a substance is directly proportional to the temperature of the substance.

Inter-conversion between States of Matter

Melting Definition
Melting is the process where a solid changes to its liquid state at a certain temperature (called the melting point) and pressure when it is heated.

  • When a solid is heated, the particles obtain energy and vibrate at a faster rate.
  • As the temperature increases, the vibration of the particles increases until they reach the melting point where the particles obtain enough energy to overcome the forces that hold them in their fixed positions.The solid then changes into a liquid.
  • During melting, the temperature remains constant. This is because the heat energy is taken in by the particles to overcome forces between them instead of being used to raise the temperature.
  • The freezing and melting points of a pure substance are the same.
Freezing Definition
Freezing is the process where a liquid changes to its solid state at a certain temperature (called freezing point) and pressure when it is cooled.

  • When a liquid is cooled, the temperature drops as heat energy is released to the surroundings.
  • As heat energy is released, the kinetic energy of the particles in the liquid decreases, causing a slower movement of particles.
  • The particles lose their energy and are pulled closer by the strong forces between the particles.
  • As the temperature keep on dropping until it reach the freezing point, the liquid start changing into solid.
  • The temperature stays constant while the liquid freezes because heat energy is released when the particles slow down to take up fixed and orderly positions in the solid.
Vaporization, also called evaporation is the process whereby atoms or molecules in a liquid state gain sufficient energy to enter the gaseous state.
Boiling is the rapid vaporization of a liquid at a certain temperature (the boiling point) and pressure when heat is applied to it.

  • Evaporation occurs below the boiling point of the liquid.
  • The particles escape from the surface of the liquid to form gas.
  • Evaporation differs from boiling in that it only takes place at the surface of the liquid and it is very slow.
  • On the other hand, boiling takes place throughout the liquid and is very fast.
  • Factors influencing rate of evaporation
  • Humidity of the air.
  • Temperature of the substance.
  • Flow rate of air.
  • Inter-molecular forces. The stronger the forces keeping the molecules together in the liquid or solid state the more energy that must be input in order to evaporate them.
  • If conditions allow the formation of vapour bubbles within a liquid, the vaporization process is called boiling.
  • When a liquid is heated, the particles gain energy and move faster.
  • As heat energy is keep on supplying to the liquid, the particles will eventually obtain enough energy to completely break the forces in between molecule.
  • The liquid then changes into a gas and particles are now able to move freely and are far apart.
  • The temperature at which this happens is called the boiling point.
  • The temperature remains constant during boiling because heat energy that is absorbed by the particles is used to break the forces holding them together.
condensation Definition
Condensation is the process by which a gas or vapor changes to liquid state at certain temperature and pressure when it is cooled.

  • When a gas is cooled, the particles lose kinetic energy.
  • As a result they move slower and this will cause the forces between them grow stronger.
  • At this point, the gas changes into liquid.
  • During condensation, heat is given out to the surroundings.
  • Condensation can occur at or below the boiling point of the substance
sublimation Definition
Sublimation is a process of conversion of a substance from the solid to the vapour state without its becoming liquid.

  • Some solids change directly into gas without becoming a liquid.
  • This process is called sublimation.
  • When heated, the particles of the solid gain enough energy to break the forces between them and move freely as a gas.
  • When cooled, the gas changes straight back to solid.
  • Examples of substances which sublime are solid carbon dioxide (dry ice), ammonium chloride and iodine.

Interesting Video:

Inter-conversion Between the 3 States of Matter

4.1b Particles in the 3 States of Matter

Matter exists in 3 states of matter, namely, solid state, liquid state and gaseous state.

Characteristics of Matter in Solid, Liquid and Gaseous State

Arrangement of Particles Particles are arranged in orderly manner and close to one another.
Particles are not arranged in order. The space between particles is moderately large.
The particles are very far apart and randomly arrange.
Movement of Particles Particles vibrate at fixed positions. Particles move randomly and slowly and sometimes will collide against each other. The particles move randomly in all directions at great speed.
Force of Attraction between particles very strong Strong but weaker than in the solid state. very weak
Ability to be compressed Very difficult to be compressed because the particles are packed closely. Not easily compressed because the particles are packed quite closely. Easily compressed because the particles are very far apart.
Volume Fixed Fixed Follows the container
Heat Energy content Lowest Energy Content Moderate energy content. Highest
energy content
Shape Fixed Follows the container Fills the whole container

Recommended Videos

States of Matter (solids, liquids and gases) | The Chemistry Journey | The Fuse School

4.1a Evidence that Matter is Made up of Particles

In SPM, you need to know
  1. diffusion is one of the proof of the particle theory of matter. 
  2. the definition of diffusion. 
  3. diffusion in solid, liquid and gas 
  4. factors that affect the rate of diffusion and the related experiments.

What is Diffusion?

1. Diffusion is a process of spreading of a substance from a region of high concentration to a region of low concentration. 
2. It occurs when the particles of the substance move through the space between the particles of another substance. 
3. Figure below shows how the bromine particles diffuse into the air. 

Diffusion occurs in solid, liquid and gas. 
5. The rate of diffusion is highest in gas and lowest in solid. 
6. Diffusion is the proof of the particle theory of matter.

  • The rate of diffusion is highest in gas and lowest in solid.
  • Diffusion is the proof of the particle theory of matter.

Diffusion in Solid

Diffusion in Solid
The blue colour of copper(II) sulphate fills up the entire test tube after a few days
  • Copper(II) sulphate crystals are made of copper(II) ions and sulphate ions which are tiny and discrete.
  • The particles in the copper(II) sulphate crystal will separate to become ions and diffuse randomly upwards until the whole agar turns blue.

Diffusion in Liquid

(Diffusion in Liquid)
The purple colour of potassium manganate(VII) fills up the entire test tube after a few hours
  • Diffusion has taken place in the liquid.
  • The rate of diffusion of the particles in water is faster than the diffusion rate of particles in solid.
  • The occurrence of diffusion proves that potassium permanganate(VII) consist of tiny and discrete particles.

Diffusion in Gas

(Diffusion in Gas)
The brown colour bromine vapour spreads evenly throughout the gas jar in a few minutes
  • Bromine vapour is made of tiny and discrete molecules that move randomly to fill up space.
  • Bromine vapour moves randomly and diffuses in all directions in air from areas of higher concentration to areas of lower concentration.

 The rate of diffusion is highest in gas and lowest in solid.

Video 1 - Diffusion

Video 2 - Diffusion in Solid

Video 3 - Diffusion in Liquid and Gas

Diffusion of Gases | The Fuse School

Brownian Motion

  1. Brownian motion is the physical phenomenon that tiny particles immersed in a fluid move about randomly.
  2. A fluid can be a liquid or a gas.
  3. Brownian movement, an example of diffusion, supports the kinetic theory of matter.
  4. Examples of Brownian movement are
    1. movement of smoke particles in air
    2. movement of pollen grains in water

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Brownian Motion

4.1 Changes in the State of Matter

Changes in the State of Matter

1. Matter is anything that occupies space and has mass.

2. Matter exists in 3 states, namely the solid state, liquid state and gaseous state.

3. We can catagorise matter into 2 categories: element and compound.

4. Element is the substance that consists of 1 type of atom. Compound is the substance that consists of more than 1 type of atom.

5. Matter is made up of a large number of tiny and discrete particles. We can catagorise the particles into 3 categories: The atoms, the molecules and the ions.

6. Atom is the smallest, indivisible particle of an element. Atoms of the same element are exactly alike and are different from the atoms of all other elements. 

7. When 2 or more atoms join together chemically, they form molecule. For example, 2 hydrogen atoms join together form a hydrogen molecule. 1 oxygen atom combine with 2 hydrogen atoms form a water molecule.

8. Ions are any particles that carry charge. For example, if a hydrogen atom is charged and carries a +1 charge, it become a hydrogen ion. Also, if an oxygen ion is charged with a charge of -2, it become an oxygen ion.

9. Ions that carry positive charge are called cations. Ions that carry negative charge are called anions. 

Kinetic Theory of Matter

The kinetic theory of matter explains the state of matter in solid, liquid and gaseous states based on the following assumptions:

1. Matter is made up of very small particles, each of which has a mass.

2. These molecules are in constant, random motion. The rapidly moving particles constantly collide with each other and with the walls of the container.

3. There are forces of attraction between particles of matter. These attraction forces will increase as the distance between the particles becomes closer.

4. The average kinetic energy of the gas particles depends only on the temperature of the system. The higher the temperature, the higher the kinetic energy of the particles.