Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 1st Term
Week: 9
Age: 15 years
Duration: 45 minutes
Subject: Chemistry
Curriculum Theme: Chemistry
Previous Lesson: Particular Nature Of Matter: Changes, Atoms And Molecules and Dalton’s Theory.
Topic: PARTICULAR NATURE OF MATTER
Subject Matter: Constituents of atoms: protons, neutrons and electrons; arrangement of electrons around the nucleus; empirical formula from percentage composition.

Specific Objectives

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

Cognitive Domain:

Identify and describe the three major constituents of an atom (protons, neutrons, and electrons).
Explain the arrangement of electrons in shells around the nucleus for simple atoms.
Calculate the empirical formula of a compound given its percentage composition.

Affective Domain:

Appreciate the structured nature of matter at the atomic level.
Show interest in understanding chemical formulas and their derivation.

Psychomotor Domain:

Draw simple diagrams showing electron arrangements in atoms.
Solve problems involving the calculation of empirical formula.

Participate in discussions about atomic structure.
Collaborate with peers to solve problems.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Senior Secondary School Chemistry.
State Unified Scheme of Work for Senior Secondary School Chemistry.
New School Chemistry for Senior Secondary Schools by Osei Yaw Ababio.

Instructional Materials

The teacher will teach this lesson with the aid of:

Atom charts showing protons, neutrons, and electrons.
Periodic table.
Worked examples sheets for empirical formula calculations.

Rationale for the Lesson

This lesson helps pupils understand the fundamental building blocks of matter and how they are arranged. Understanding atomic structure and electron arrangement is important for explaining chemical bonding and reactions. Knowing how to derive empirical formulas helps pupils determine the simplest ratio of elements in a compound, which is a key skill in quantitative chemistry.

Prerequisite/Previous Knowledge

Pupils should have prior knowledge of the concept of matter, elements, compounds, and mixtures from their junior secondary school science classes.

Lesson Content/Board Summary

PARTICULAR NATURE OF MATTER

Constituents of Atoms: Protons, Neutrons, and Electrons

An atom is the smallest particle of an element that can take part in a chemical reaction. Atoms are made up of smaller particles called sub-atomic particles.

The three main sub-atomic particles are:

Protons: Positively charged particles found in the nucleus. They have a relative mass of 1 atomic mass unit (amu). The number of protons determines the atomic number (Z) and the identity of the element.
Neutrons: Neutral particles (no charge) found in the nucleus. They have a relative mass of 1 atomic mass unit (amu). Neutrons contribute to the mass number but not the charge of the atom.
Electrons: Negatively charged particles that orbit the nucleus in specific energy levels or shells. They have a negligible relative mass (approximately 1/1836 amu). In a neutral atom, the number of electrons equals the number of protons.

Arrangement of Electrons Around the Nucleus (Electron Configuration)

Electrons are arranged in distinct energy levels or shells around the nucleus. These shells are designated K, L, M, N, etc., or by numbers 1, 2, 3, 4, respectively. Each shell can hold a maximum number of electrons.

The maximum number of electrons in a shell is given by the formula 2n², where ‘n’ is the shell number:

K-shell (n=1): Maximum 2(1)² = 2 electrons.
L-shell (n=2): Maximum 2(2)² = 8 electrons.
M-shell (n=3): Maximum 2(3)² = 18 electrons.
N-shell (n=4): Maximum 2(4)² = 32 electrons.

Electrons fill the shells starting from the innermost shell (K-shell) outwards. The outermost electrons are called valence electrons and determine the chemical properties of an element.

Examples:

Sodium (Na, Atomic number = 11): Electron configuration is 2, 8, 1.
Chlorine (Cl, Atomic number = 17): Electron configuration is 2, 8, 7.

Empirical Formula from Percentage Composition

The empirical formula is the simplest whole-number ratio of atoms of each element in a compound.

To calculate the empirical formula from percentage composition, the following steps are generally followed:

Step 1: Assume 100g of the compound. This converts percentages directly into grams.
Step 2: Convert the mass of each element to moles by dividing by its atomic mass.
Step 3: Divide each mole value by the smallest mole value obtained in Step 2 to get the simplest ratio.
Step 4: If the ratios are not whole numbers, multiply all ratios by the smallest integer that converts them into whole numbers.
Step 5: Write the empirical formula using these whole-number ratios as subscripts for each element.

Example: A compound contains 40.0% Carbon, 6.7% Hydrogen, and 53.3% Oxygen. Determine its empirical formula. (Atomic masses: C=12, H=1, O=16)

Solution:

Carbon (C): 40.0 g / 12 g/mol = 3.33 mol
Hydrogen (H): 6.7 g / 1 g/mol = 6.7 mol
Oxygen (O): 53.3 g / 16 g/mol = 3.33 mol

Divide by the smallest mole value (3.33):

C: 3.33 / 3.33 = 1
H: 6.7 / 3.33 ≈ 2
O: 3.33 / 3.33 = 1

The empirical formula is CH₂O.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and reviews the previous lesson briefly. The teacher then asks questions like: “What is the smallest unit of an element?” and “What do you know about atoms?” The teacher introduces the topic “Particular Nature of Matter” and states the lesson objectives.
Pupils’ Activity: Pupils respond to questions and listen attentively to the introduction.
Learning Point: Pupils recall prior knowledge and are prepared for the new topic.

Step 2: Constituents of Atoms

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher uses an atom chart to explain the three main sub-atomic particles: protons, neutrons, and electrons. The teacher describes their location, charge, and relative masses. The teacher guides pupils to identify these parts and their charges.
Pupils’ Activity: Pupils observe the chart, listen to explanations, and identify the parts of an atom as guided by the teacher.
Learning Point: Pupils understand the fundamental components of an atom.

Step 3: Arrangement of Electrons

Time: 10 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher explains how electrons are arranged in shells around the nucleus, using the 2n² rule. The teacher demonstrates the electron arrangement for simple atoms like Sodium and Chlorine on the board, drawing simple diagrams. The teacher emphasizes the importance of valence electrons.
Pupils’ Activity: Pupils observe the illustrations, take notes, and practice arranging electrons for simple atoms as guided by the teacher.
Learning Point: Pupils learn about electron shells and how electrons are distributed in atoms.

Step 4: Introduction to Empirical Formula

Time: 5 minutes
Teaching Skill: Definition/Concept Introduction
Teacher’s Activity: The teacher defines empirical formula as the simplest whole-number ratio of atoms in a compound. The teacher explains why it is important in chemistry to determine the empirical formula from experimental data.
Pupils’ Activity: Pupils listen, ask questions for clarity, and write down the definition.
Learning Point: Pupils understand what empirical formula is and its significance.

Step 5: Calculating Empirical Formula from Percentage Composition

Time: 10 minutes
Teaching Skill: Problem Solving/Demonstration
Teacher’s Activity: The teacher outlines the steps for calculating empirical formula from percentage composition. The teacher works through the example provided in the lesson content (40.0% Carbon, 6.7% Hydrogen, 53.3% Oxygen) step-by-step on the board, explaining each stage clearly. The teacher encourages questions.
Pupils’ Activity: Pupils observe the steps, ask questions, and follow along by working the example in their notebooks.
Learning Point: Pupils learn the systematic approach to calculating empirical formulas.

Step 6: Practice and Application

Time: 5 minutes
Teaching Skill: Guided Practice
Teacher’s Activity: The teacher provides another simple example for pupils to attempt in pairs or individually, circulating to provide assistance and check understanding. For instance: “A compound contains 80% Carbon and 20% Hydrogen. Find its empirical formula.”
Pupils’ Activity: Pupils work on the practice problem. A few pupils present their solutions on the board.
Learning Point: Pupils apply the learned steps to solve new problems.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

Mention the three main sub-atomic particles and state their charges.
Explain how electrons are arranged in shells around the nucleus.
What is an empirical formula?
A compound contains 92.3% Carbon and 7.7% Hydrogen. Calculate its empirical formula. (C=12, H=1)

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, reinforcing the concepts of atomic constituents, electron arrangement, and empirical formula. The teacher gives pupils homework related to calculating empirical formulas.
Pupils’ Activity: Pupils listen to the summary and copy down the homework assignment.
Learning Point: Pupils consolidate their understanding of the topic.

Lesson Keywords

Atom – The smallest particle of an element.
Proton – Positively charged sub-atomic particle in the nucleus.
Neutron – Neutral sub-atomic particle in the nucleus.
Electron – Negatively charged sub-atomic particle orbiting the nucleus.
Nucleus – The central part of an atom containing protons and neutrons.
Electron Shell – Energy levels where electrons are found.
Empirical Formula – The simplest whole-number ratio of atoms in a compound.
Percentage Composition – The percentage by mass of each element in a compound.

Differentiation

For pupils who grasp concepts quickly, the teacher can provide more complex problems involving molecular formula derivation after finding the empirical formula. For pupils who need more support, the teacher can provide additional guided practice with simpler examples and step-by-step prompts for calculations.

Note for teachers using this lesson plan

Ensure that atom charts are clear and visible to all pupils. Emphasize the practical application of empirical formula calculation in chemical analysis. Encourage pupils to ask questions and to work collaboratively on problem-solving tasks. Provide ample practice problems for empirical formula calculations.