Subject : Chemistry


Topic :



Class :

SS 1


Term :

1st Term / First Term


Week :

Week 2


Instructional Materials :

  • Lagos State Scheme of Work
  • Textbooks On Social Studies
  • Online Materials
  • Picture Charts



Previous Knowledge :

The pupils have been taught

Introduction to Chemistry

in their previous lesson


Behavioural Objectives :  At the end of the lesson, the pupils should be able to

  • Explain physical and chemical changes
  • State the elements and their symbols.
  • Define Atoms, molecules, atomicity
  • List three sub atomic particles with their corresponding charges.
  • State four Dalton’s atomic theory with their modifications.






  1. Physical and chemical changes
  2. Elements and their symbols.
  3. Atoms, molecules, atomicity
  4. Dalton’s atomic theory



DEFINITION: A Physical change is one which is easily reversed and in which no new substances are formed.


  1. Melting of solids to liquids.
  2. Freezing of liquids to solids.
  3.  Vaporization of liquids to gases.
  4. Liquefaction of gases to liquids.
  5. Sublimation of solids to vapour.


DEFINITION: A chemical change is one which is not easily reversed and in which a new substance is formed.


  1. Burning of substances.
  2. Dissolution of metals and limestone in acids. 
  3. Chemical decomposition – like digestion of food. 
  4. Rusting of iron.
  5. Charring of sugar.
  6. Dissolution of metals in acids.


1) Physical changes are usually reversible, while chemical changes are not.

2) Physical changes do not involve a change in the chemical composition of a substance, while chemical changes do.

3) Physical changes typically involve changes in the physical properties of a substance, while chemical changes involve changes in its chemical properties.

4) Energy is usually required for physical changes, while chemical changes usually involve the release or absorption of energy.

5) Physical changes are often caused by external factors such as heat, light, or pressure, while chemical changes are usually caused by a reaction between two or more substances.

6) Physical changes usually occur gradually, while chemical changes often occur rapidly.

7) Physical changes are usually easily observed, while chemical changes may not be.

8) Physical changes usually do not result in the formation of new substances, while chemical changes often do.

9) Physical changes can usually be reversed, while chemical changes generally cannot.

10) In physical changes, the original substance(s) retain their chemical identity, while in chemical changes, the original substance(s) are changed into new substances with different chemical identities.

11) Many physical changes (such as melting, freezing, and boiling) involve a change in state but not a chemical reaction, while all chemical changes involve a chemical reaction.

12) Some physical changes (such as dissolving) involve a change in physical properties but not a change in state, while all chemical changes involve a change in chemical properties.


  1. Mention three familiar process/changes which you know to be:(a) Physical changes (b) chemical changes.
  2. List three differences between physical change and chemical change.
  3. Classify each of the following as physical change or chemical change.(a) Boiling of egg (b) Burning of kerosene (c) Melting of wax (d) Rusting of iron(e) Digestion of glucose (f) Dissolving iron in an acid.
  1. State with a reason in each case whether each of the following is physical or chemical change.
  1. Dissolving common salt in water.
  2. Burning of petrol.
  3. Digestion of glucose.



An element is a substance that cannot be broken into simpler substances by any chemical methods. Examples of elements include: Iron, tin, aluminum etc.

There are about 118 known elements of which 92 are naturally exiting elements and the rest are artificially made.

Symbols are modern ways of representing atoms of elements by using abbreviations. The modern symbols were developed by Berzelius in 1814.

First, He used the first letter in the name of the element.


Hydrogen H
Boron B
Carbon C
Nitrogen N
Oxygen O
Fluorine F
Phosphorus P
Sulphur S
Iodine I

The second principle uses the first two letters.



    Helium    He

    Lithium    Li

    Beryllium    Be

    Neon    Ne

Aluminum    Al Silicon    Si

    Argon    Ar

    Calcium    Ca

    Bromine    Br

    Barium    Ba

The third principle is when the first letter and another letter in the name are used.


ELEMENTS    SYMBOL Magnesium    Mg

    Chlorine    Cl

    Chromium    Cr

    Manganese    Mn

    Zinc    Zn

The fourth principle is the elements that derived symbols from their Latin names.


ELEMENT    LATIN NAME    SYMBOL Sodium    Natrium    Na

    Potassium    Kalium    K

    Iron    Ferrum    Fe


Copper Cuprum Cu
Silver Argentum Ag
Tin Stannum Sn
Gold Aurum Au
Mercury Hydrargyrum Hg
Lead Plumbum Pb



DEFINITION: An atom is the smallest particle of an element which can take part in a chemical reaction.


An atom is made up of the three sub-particles known as protons, neutrons and electrons as shown in the diagram below. Their characteristics are also summarized in the table below:




Proton Nucleus + 1 p
Electron Outside nucleus _ 0.005 e
Neutron Nucleus Zero 1 n


DEFINITION: A molecule is the smallest particle of a substance that normally exist alone and still retain the chemical properties of that substance be it an element or a compound.

Some molecules can exist independently as single atoms e.g. He, Ne, Ar, Xe etc. Some molecules may be made up of atoms of the same element e.g. a molecule of hydrogen is H2, that of chlorine is Cl2, Oxygen is O2, phosphorus is P4, Sulphur is S8.Some molecules may be made up of different elements e.g. a molecule of water is H2O, Methane is CH4, ammonia is NH3, carbon (iv) oxide is CO2 etc.

ATOMICITY: Atomicity is the number of atoms in each molecule of an element.

Atomicity of some molecules


Element Formula molecule of Atomicity
Hydrogen H2 2
Oxygen O2 2
Ozone O3 3
Phosphorus P4 4
Sulphur S8 8
Chlorine Cl2 2
Neon Ne 1
Argon Ar 1
Tetraoxosulphate(vi) acid H2SO4 7
Amonium tetraoxosulphate(vi) (NH4)2SO4 15


In 1808 John Dalton proposed the following Atomic theory.

  1. All elements are made up of small indivisible particles called atoms.
  2. Atoms can neither be created or destroyed
  3. Atoms of the same element are alike in every aspect, and differ from atoms of all other elements.
  4. When atoms combine with other atoms, they do so in simple ratios.
  5. All chemical changes result from the combination or the separation of atoms.



1) Discovery of subatomic particles:

Dalton’s atomic theory was based on the concept that atoms are indivisible and indestructible. However, the discovery of subatomic particles like electrons, protons and neutrons proved that atoms are not indivisible.

2) Discovery of radioactivity:

The discovery of radioactivity by Henri Becquerel in 1896 showed that atoms are not indestructible. Radioactive atoms decay into other atoms over time.

3) Discovery of the nuclear model of the atom:

Ernest Rutherford’s gold foil experiment in 1911 led to the discovery of the nuclear model of the atom. This model showed that atoms are mostly empty space with a tiny, dense nucleus at the center.

4) Discovery of quantum mechanics:

Quantum mechanics is a branch of physics that studies the behavior of matter and energy on the atomic and subatomic level. The discovery of quantum mechanics in the early 20th century showed that atoms are not really indivisible after all.

5) Discovery of the wave-particle duality:

The wave-particle duality is a central principle of quantum mechanics that states that particles can exhibit both wave-like and particle-like behavior depending on the experimental setup. This discovery showed that our understanding of atoms is still evolving and that they are even more mysterious than we thought.

Despite these modifications, Dalton’s atomic theory is still considered to be one of the most important achievements in the history of science. It laid the foundation for our modern understanding of atoms and paved the way for many other important discoveries in physics and chemistry. Atomic theory is an important part of our scientific heritage and will continue to be so for many years to come.

Thank you for your attention. I hope this has been helpful. Please let me know if you have any questions.


Dr. Quantum


1) What were the modifications made to Dalton’s atomic theory?

2) Why were these modifications necessary?

3) What did the discovery of subatomic particles prove?

4) What did the discovery of radioactivity show?

5) What was the impact of Rutherford’s gold foil experiment?

6) What is quantum mechanics?

7) What is the wave-particle duality?

8) How has our understanding of atoms changed over time?

9) Why is Dalton’s atomic theory still important today?

10) What does the future hold for atomic theory?


  1. What are the three fundamental units of all matter? Give their relative masses and charges.
  2. Describe their relative positions to one another in an atom.
  3. Name the two main part of an atom?
  4. Mention the three subatomic particles in an atom.
  5. Which particles are found in each part of the atom?
  6. List three sub atomic particles with their corresponding charges.
  7. State four Dalton’s atomic theory with their modifications.


The electronic configuration of the first twenty element using the concept of K,L,M,N and the sub-energy atomic level configuration i.e. s,p,d,f.


1. H: 1s1

2. He: 1s2

3. Li: 1s2 2s1

4. Be: 1s2 2s2

5. B: 1s2 2s2 2p1

6. C: 1s2 2s2 2p2

7. N: 1s2 2s2 2p3

8. O: 1s2 2s2 2p4

9. F: 1s2 2s2 2p5

10. Ne: 1s2 2s2 2p6

11. Na: 1s2 2s2 2p6 3s1

12. Mg: 1s2 2s2 2p6 3s2

13. Al: 1s2 2s2 2p6 3s2 3p1

14. Si: 1s2 2s2 2p6 3s2 3p2

15. P: 1s2 2s2 2p6 3s2 3p3

16. S: 1s2 2s2 2p6 3s2 3p4

17. Cl: 1s2 2s2 2p6 3s2 3p5

18. Ar: 1s2 2s2 2p6 3s2 3p6

19. K: 1s2 2s2 2p6 3s2 3p6 4s1

20. Ca: 1s2 2s2 2p6 3s2 3p6 4s2



  1. The simplest unit of Matter that retains its properties is called. (a) an atom (b) an element (c) an hydroxide (c) a molecule
  2. Of the basic particles that make up an atom, the one with the smallest mass is? (a) a proton (b) a neutron (c) an x- particle (d) an electron
  3. The following are physical changes except: (a) melting of candle wax (b) Dissolving common salt in water (c) Freezing of water (d) Rotting of leaves.
  4. Which of the following is not a molecule of the same element. (a) O2(b) P4 (c) S8 (d)CO2
  5. The atomicity of O3 is (a) 1 (b) 2 (c) 3 (d )4


  1. Write four examples in each case of (a) Physical change (b) Chemical change
  2. Define the following giving two examples in each case. (a) Atom (b) Ion
  3. Write the symbols for proton, electron and neutrons.
  4. Define atomicity giving two examples.
  5. Write four Dalton’s atomic theory.


Write the electronic configuration of the first twenty element using the concept of K,L,M,N and the sub-energy atomic level configuration i.e. s,p,d,f.




The topic is presented step by step


Step 1:

The class teacher revises the previous topics


Step 2.

He introduces the new topic


Step 3:

The class teacher allows the pupils to give their own examples and he corrects them when the needs arise


Evaluation :

1. What is Chemistry?

2. What are the five major branches of chemistry?

3. What are the four most common elements in the universe?

4. What are atoms and what are their basic structure?

5. How do chemical bonds form?

6. What are the properties of molecules?

7. What are the states of matter?

8. What are solutions and how do they form?

9. What is an acid and what is a base?

10. What are redox reactions and how do they occur?

11. What is radioactivity and what are its dangers?

12. What are the uses of nuclear chemistry?

Conclusion :

The class teacher gives out ó brief note that is based on the topic that has just been taught.


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