Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 2nd Term
Week: 4
Age: 15 years
Duration: 45 minutes
Subject: Chemistry
Curriculum Theme: Chemistry
Previous Lesson: Chemical Combination: States Of Matter and Kinetic Theory.
Topic: Symbols, Formulae and Equation
Subject Matter: Chemical symbols of elements and their valencies, empirical and molecular formulae, law of conservation of matter, and balancing chemical equations

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

define chemical symbol, valency, empirical formula, molecular formula, and chemical equation.
state common symbols of elements and their valencies using the periodic table.
write correct chemical formulae from given valencies.
calculate empirical and molecular formulae from simple data.
state the law of conservation of matter and relate it to balancing equations.

Affective Domain:

show accuracy and neatness when writing symbols, formulae, and equations.
demonstrate a careful attitude during simple laboratory activities.

Psychomotor Domain:

use the periodic table to identify symbols and write correct valencies.
balance simple chemical equations by adjusting coefficients.
carry out a simple closed-system experiment to observe conservation of mass and record results.

work cooperatively in pairs/groups to solve formula and equation problems.
share results and compare answers respectfully during class discussion.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum (NERDC).
State Unified Scheme of Work.
Ababio, O. Y. New School Chemistry for Senior Secondary Schools.
OpenStax Chemistry 2e, “Writing and Balancing Chemical Equations.”
Khan Academy, “Balancing chemical equations” (article/lesson).
Nigeria Federal Ministry of Education (Inspire), lesson preview on “Symbols, Formulae and Equations.”
Royal Society of Chemistry, practical resources on conservation of mass in closed systems.

Instructional Materials

The teacher will teach this lesson with the aid of:

Periodic table of elements (wall chart or handouts).
Coloured beads (to model atoms/ions and show ratios in formulae).
Whiteboard/marker or chalkboard/chalk.
Measuring balance (or any mass measuring device available).
Conical flask or plastic bottle, balloon, vinegar and baking soda (for conservation of mass demonstration).
Calculator and simple data worksheet for empirical/molecular formulae.

Rationale for the Lesson

Writing correct symbols, formulae, and equations helps pupils to represent substances and reactions clearly in Chemistry. Balancing equations and understanding conservation of mass enables pupils to solve calculation questions and explain what happens during chemical reactions in daily life and in the laboratory.

Prerequisite/Previous Knowledge

Pupils have learned common elements, atoms and molecules, and can read basic information from the periodic table such as element names and symbols.

Lesson Content/Board Summary

SYMBOLS, FORMULAE AND EQUATION

Chemical Symbols

A chemical symbol is the short form used to represent an element. It is usually one or two letters, with the first letter written in capital and the second in small letter (if present).

The following are examples of chemical symbols:

Hydrogen: H
Oxygen: O
Carbon: C
Sodium: Na
Calcium: Ca
Chlorine: Cl
Iron: Fe
Copper: Cu

Valency of Elements

Valency is the combining power of an atom of an element. It shows the number of electrons an atom loses, gains, or shares during bonding.

The following are common elements and their valencies:

Hydrogen (H): 1
Oxygen (O): 2
Nitrogen (N): 3
Carbon (C): 4
Sodium (Na): 1
Magnesium (Mg): 2
Aluminium (Al): 3
Chlorine (Cl): 1
Calcium (Ca): 2
Iron (Fe): 2 or 3

Writing Chemical Formulae from Valencies

A chemical formula shows the types of elements present in a compound and the number of atoms of each element in the compound.

The following are rules for writing chemical formulae:

Write the symbol of the positive ion (metal) first, then the negative ion (non-metal) second.
Write the valency of each ion.
Cross the valencies to become subscripts (do not write the charges).
Reduce the subscripts to the simplest whole-number ratio.

The following are examples of chemical formulae written from valencies:

Na (1) and Cl (1) gives NaCl
Mg (2) and Cl (1) gives MgCl₂
Al (3) and O (2) gives Al₂O₃
Ca (2) and O (2) gives CaO

Empirical Formula

Empirical formula is the simplest whole-number ratio of the atoms of the elements in a compound.

The following are steps for calculating empirical formula from percentage composition:

Assume total mass = 100 g and change percentages to grams.
Convert each mass to moles by dividing by relative atomic mass.
Divide all mole values by the smallest mole value to get a ratio.
Multiply all ratios by a whole number if needed to obtain whole numbers.
Write the empirical formula using the whole-number ratio as subscripts.

Molecular Formula

Molecular formula shows the actual number of atoms of each element in one molecule of a compound.

The following is the relationship between molecular formula and empirical formula:

Molecular formula = (Empirical formula)ⁿ
n = (Molar mass of compound) ÷ (Empirical formula mass)

Chemical Equations

A chemical equation is a symbolic representation of a chemical reaction using chemical formulae of reactants and products.

The following are parts of a chemical equation:

Reactants: substances on the left-hand side of the arrow
Products: substances on the right-hand side of the arrow
Arrow (→): shows the direction of the reaction
Coefficients: numbers placed before formulae to show the number of molecules or moles

Law of Conservation of Matter (Mass)

The law of conservation of matter states that matter is neither created nor destroyed during a chemical reaction. In a closed system, the total mass of reactants equals the total mass of products. :contentReference[oaicite:4]{index=4}

The following are implications of the law in chemical equations:

The number of atoms of each element must be the same on both sides of the equation.
Balancing chemical equations is required to obey the law of conservation of matter.

Balancing Chemical Equations

Balancing a chemical equation is the process of adjusting coefficients so that each element has the same number of atoms on both the reactant and product sides. :contentReference[oaicite:5]{index=5}

The following are steps for balancing chemical equations:

Write the correct formulae for all reactants and products.
Count the number of atoms of each element on both sides.
Place coefficients in front of formulae to balance one element at a time.
Recount atoms after each change until all elements are balanced.
Ensure the final coefficients are the smallest whole numbers.

The following are examples of balanced equations:

2H₂ + O₂ → 2H₂O
Zn + 2HCl → ZnCl₂ + H₂
2Mg + O₂ → 2MgO

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Guided Practice, Problem Solving, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher revises the idea of elements and the periodic table, then displays a few element names and asks pupils to provide their symbols. The teacher introduces the topic as symbols, formulae and equations and states the lesson focus areas.
Pupils’ Activity: Pupils respond with symbols, identify common elements on the periodic table, and listen to the lesson focus.
Learning Point: Symbols are used to represent elements.

Step 2: Chemical Symbols and Valencies

Time: 7 minutes
Teaching Skill: Explanation and Questioning
Teacher’s Activity: The teacher explains chemical symbols and valency, guides pupils to locate symbols and common valencies from the periodic table, and writes examples on the board.
Pupils’ Activity: Pupils write selected symbols and valencies from the periodic table and read them aloud when called upon.
Learning Point: Elements have symbols and valencies used for writing formulae.

Step 3: Writing Chemical Formulae

Time: 7 minutes
Teaching Skill: Demonstration and Guided Practice
Teacher’s Activity: The teacher demonstrates how to write formulae using valencies (cross-over method) and uses coloured beads to model simple ratios in compounds. The teacher gives examples for pupils to attempt.
Pupils’ Activity: Pupils write formulae for given pairs of elements/ions and compare answers in pairs.
Learning Point: Chemical formulae are written from correct symbols and valencies.

Step 4: Empirical Formula

Time: 7 minutes
Teaching Skill: Worked Example and Problem Solving
Teacher’s Activity: The teacher explains empirical formula and guides pupils through one worked example using simple data (mass/percentage). The teacher highlights the steps: convert to moles, divide by smallest, and obtain whole-number ratio.
Pupils’ Activity: Pupils follow the example, solve a short class exercise, and write the final empirical formula in their notebooks.
Learning Point: Empirical formula shows the simplest ratio of atoms in a compound.

Step 5: Molecular Formula

Time: 6 minutes
Teaching Skill: Explanation and Application
Teacher’s Activity: The teacher explains molecular formula and the relationship between empirical and molecular formula using n = molar mass ÷ empirical formula mass. The teacher guides pupils through one simple example.
Pupils’ Activity: Pupils calculate n for a given example and write the molecular formula correctly.
Learning Point: Molecular formula gives the actual number of atoms in a molecule.

Step 6: Conservation of Mass Demonstration

Time: 5 minutes
Teaching Skill: Demonstration and Observation
Teacher’s Activity: The teacher performs a closed-system experiment (e.g., vinegar in a flask/bottle and baking soda placed in a balloon, then sealed). The teacher measures mass before and after mixing and guides pupils to observe that mass remains the same in a closed system.
Pupils’ Activity: Pupils observe carefully, record mass values, and state what they notice about mass before and after the reaction.
Learning Point: In a closed system, mass is conserved during chemical reactions.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define chemical symbol and give two examples.
State the meaning of valency and write the valencies of Na, O, and Al.
Write the chemical formula for magnesium chloride and aluminium oxide.
Explain the law of conservation of matter and state why equations must be balanced.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 3 minutes
Teaching Skill: Summary and Reinforcement
Teacher’s Activity: The teacher summarizes the key points on symbols, valency, formulae, conservation of mass, and balancing equations. The teacher gives a brief assignment on balancing simple equations and writing formulae from valencies.
Pupils’ Activity: Pupils listen, ask final questions, and copy the assignment.
Learning Point: Correct symbols and valencies support correct formulae and balanced equations.

Lesson Keywords

Chemical symbol – the short form used to represent an element.
Valency – the combining power of an element in forming compounds.
Chemical formula – the representation showing elements and the number of atoms in a compound.
Empirical formula – the simplest whole-number ratio of atoms in a compound.
Molecular formula – the actual number of atoms of each element in a molecule.
Chemical equation – the symbolic representation of a chemical reaction using formulae.
Balancing – adjusting coefficients so atoms of each element are equal on both sides of an equation.
Conservation of mass – the rule that mass remains constant in a closed system during a reaction.

Differentiation

Pupils who need support will be guided with a valency table and step-by-step templates for formula writing and balancing. Pupils who learn faster will solve additional problems involving empirical/molecular formula calculations and more balanced equations for class discussion.

Note for teachers using this lesson plan

Use the periodic table frequently so pupils build the habit of checking symbols and valencies correctly. During the conservation of mass activity, ensure the system is properly closed and emphasize safety and accurate measurement. Keep board work neat and exam-focused, and give enough practice questions for mastery.