Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: First Term
Week: 10
Age: 15 years
Duration: 45 minutes
Subject: Chemistry
Curriculum Theme: Chemistry
Previous Lesson: Particular Nature Of Matter: Subatomic Particles, Electron Arrangement and Empirical.
Topic: PARTICULAR NATURE OF MATTER
Subject Matter: atomic number, mass number and isotopy, relative atomic masses based on C-12 isotope, relative molecular mass calculations for compounds

Specific Objectives

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

Cognitive Domain:

Define atomic number, mass number, and isotopy.
State the reference isotope for relative atomic mass.
Identify isotopes from given data.

Affective Domain:

Appreciate the importance of these concepts in understanding the composition of matter.
Participate actively in classroom discussions.

Psychomotor Domain:

Solve problems involving atomic number and mass number.
Calculate relative atomic mass given isotopic abundances.
Calculate relative molecular mass for various compounds from their formulae.

Collaborate with peers in solving numerical problems.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Senior Secondary Schools.
State Unified Scheme of Work for Chemistry, SSS 1.
New School Chemistry for Senior Secondary Schools by Osei Yaw Ababio.

Instructional Materials

The teacher will teach this lesson with the aid of:

A periodic table.
Calculators.
Practice questions on atomic structure and relative masses.
Whiteboard and markers.

Rationale for the Lesson

This lesson helps pupils understand the fundamental building blocks of matter and how elements are identified and measured. Knowing atomic number, mass number, and how to calculate relative masses is important for further studies in chemistry, allowing pupils to predict how substances combine and react.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of atoms, elements, protons, neutrons, and electrons, and the concept of chemical symbols from previous lessons.

Lesson Content/Board Summary

Particular Nature of Matter

Atomic Number (Z)

The atomic number (Z) of an element is the number of protons in the nucleus of an atom of that element. It determines the identity of an element. In a neutral atom, the number of protons is equal to the number of electrons.

Example: Carbon (C) has an atomic number of 6, meaning it has 6 protons.

Mass Number (A)

The mass number (A) of an atom is the total number of protons and neutrons in its nucleus. It represents the approximate mass of the atom.

Mass Number (A) = Number of Protons (Z) + Number of Neutrons (N)

Number of Neutrons (N) = Mass Number (A) – Atomic Number (Z)

Example: An atom with 6 protons and 6 neutrons has a mass number of 12.

Isotopy

Isotopes are atoms of the same element (having the same atomic number) but with different mass numbers due to a different number of neutrons.

The following are characteristics of isotopes:

They have the same number of protons.
They have the same number of electrons (in a neutral atom).
They have different numbers of neutrons.
They have the same chemical properties.
They have different physical properties (e.g., density, mass).

Examples:

Hydrogen has three isotopes: Protium (¹₁H), Deuterium (²₁H), Tritium (³₁H).
Chlorine has two common isotopes: Chlorine-35 (³⁵₁₇Cl) and Chlorine-37 (³⁷₁₇Cl).

Relative Atomic Mass (RAM)

Relative atomic mass (RAM) of an element is the average mass of an atom of the element compared to 1/12th the mass of an atom of carbon-12 isotope.

The following are important points about RAM:

The reference isotope is carbon-12 (¹²C).
It is an average because most elements exist as a mixture of isotopes.
It has no unit.

Calculation of RAM:

RAM = [(% abundance of isotope 1 × mass of isotope 1) + (% abundance of isotope 2 × mass of isotope 2)] / 100

Example: If Chlorine-35 has 75% abundance and Chlorine-37 has 25% abundance:

RAM of Cl = [(75 × 35) + (25 × 37)] / 100 = (2625 + 925) / 100 = 3550 / 100 = 35.5

Relative Molecular Mass (RMM)

Relative molecular mass (RMM) is the sum of the relative atomic masses of all the atoms present in one molecule of a compound.

The following are steps to calculate RMM:

Identify the chemical formula of the compound.
Find the relative atomic mass (RAM) of each element from the periodic table.
Multiply the RAM of each element by the number of its atoms in the formula.
Sum up all the values obtained.

Example: Calculate the RMM of H₂SO₄ (Given: H=1, S=32, O=16)

RMM of H₂SO₄ = (2 × RAM of H) + (1 × RAM of S) + (4 × RAM of O)

= (2 × 1) + (1 × 32) + (4 × 16)

= 2 + 32 + 64

= 98

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 on basic atomic structure. The teacher then asks pupils what they know about the composition of different elements. The teacher introduces the topic “Particular Nature of Matter” and writes it on the board.
Pupils’ Activity: Pupils respond to questions and listen attentively.
Learning Point: Pupils recall prior knowledge and are prepared for the new topic.

Step 2: Explanation of Atomic Number and Mass Number

Time: 10 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher defines atomic number (Z) as the number of protons and mass number (A) as the sum of protons and neutrons. The teacher uses examples from the periodic table to illustrate these concepts, showing how to determine the number of neutrons.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification. They practice determining the number of protons, neutrons, and electrons for given elements.
Learning Point: Pupils understand how to identify atomic number, mass number, and derive the number of subatomic particles.

Step 3: Explanation of Isotopy

Time: 8 minutes
Teaching Skill: Explanation/Comparison
Teacher’s Activity: The teacher defines isotopes and explains why they have the same chemical properties but different physical properties. The teacher provides common examples like hydrogen and chlorine isotopes.
Pupils’ Activity: Pupils identify isotopes from given data and note down examples.
Learning Point: Pupils understand the concept of isotopes and their characteristics.

Step 4: Explanation of Relative Atomic Mass (RAM)

Time: 7 minutes
Teaching Skill: Explanation/Calculation
Teacher’s Activity: The teacher explains relative atomic mass, emphasizing carbon-12 as the standard reference. The teacher demonstrates how RAM is calculated from the isotopic abundances of an element using a simple example.
Pupils’ Activity: Pupils listen, take notes, and observe the calculation process.
Learning Point: Pupils understand the definition and calculation method of relative atomic mass.

Step 5: Explanation of Relative Molecular Mass (RMM)

Time: 7 minutes
Teaching Skill: Demonstration/Calculation
Teacher’s Activity: The teacher defines relative molecular mass and uses the periodic table to demonstrate how to calculate it for compounds like H₂SO₄, CO₂, and H₂O. The teacher guides pupils through the steps.
Pupils’ Activity: Pupils follow the calculations, ask questions, and attempt simple calculations.
Learning Point: Pupils learn how to calculate the relative molecular mass of compounds.

Step 6: Worked Examples/Practice

Time: 8 minutes
Teaching Skill: Problem Solving/Application
Teacher’s Activity: The teacher provides additional practice questions on calculating RMM for various compounds and identifying isotopes. The teacher walks around to assist pupils as they work.
Pupils’ Activity: Pupils work individually or in pairs to solve the practice problems.
Learning Point: Pupils apply their knowledge to solve related 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:

Define atomic number and mass number.
What are isotopes? Give two examples.
State the reference isotope used for determining relative atomic mass.
Calculate the relative molecular mass of glucose (C₆H₁₂O₆). (Given: C=12, H=1, O=16)

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, reiterating the importance of understanding atomic number, mass number, isotopy, and relative masses in chemistry. The teacher gives homework, which includes calculating RMM for other compounds.
Pupils’ Activity: Pupils listen to the summary and copy down the homework.
Learning Point: Pupils reinforce their understanding and prepare for future learning.

Lesson Keywords

Atomic Number – The number of protons in an atom’s nucleus.
Mass Number – The total number of protons and neutrons in an atom’s nucleus.
Isotopes – Atoms of the same element with different numbers of neutrons.
Relative Atomic Mass (RAM) – The average mass of an atom of an element compared to 1/12th the mass of a carbon-12 atom.
Relative Molecular Mass (RMM) – The sum of the relative atomic masses of all atoms in a molecule.

Differentiation

For pupils who grasp concepts quickly, challenging problems involving more complex molecular structures or calculations of average atomic mass from percentage abundances will be provided. For pupils who need more support, the teacher will provide simplified examples, offer one-on-one guidance, and encourage peer-to-peer tutoring. Visual aids and step-by-step calculation guides will be available to all.

Note for teachers using this lesson plan

Ensure that pupils have access to periodic tables and calculators throughout the lesson, especially during the practice and evaluation stages. Emphasize the importance of clear working steps when calculating relative molecular masses. Encourage pupils to ask questions and participate actively to ensure a solid foundation in these fundamental concepts.