Electronic Configuration of the First 20 Elements and Basic Atomic Terms for SS 1

Class: SS 1
Term: Second Term
Week: 6
Age: 15 years
Duration: 60 minutes
Subject: Chemistry
Curriculum Theme: The chemical world
Focal competence: Determining the relative atomic masses
Key competencies/values: Creativity and Innovation; ICT and Digital Competencies; Digital Competencies; Innovation
Skills:

• Making models of electronic configuration of atoms
• Calculating relative atomic masses from isotopic data

Previous Lesson: Atomic Structure, Constituents of the Atom and Properties of Subatomic Particles
Topic: Atomic Structure: Electronic Configuration Of The Atoms Of The First 20 Elements
Subject Matter: Definitions of atomic number, mass number, isotopes and relative atomic mass

Specific Objectives

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

Cognitive Domain

• Differentiate among atomic number, mass number, and isotopes.
• Calculate relative atomic masses from isotopic data.
• Describe the electronic configuration of the atoms of the first 20 elements.

Affective Domain

• Appreciate the importance of electronic configuration in understanding chemical properties.
• Participate actively in group discussions on atomic terms.

Psychomotor Domain

• Construct simple models or diagrams illustrating electronic configurations.
• Demonstrate the calculation of relative atomic mass using given data.

Social Domain

• Collaborate effectively in small groups to explain atomic concepts.

Reference Materials

The following resources were used in planning this lesson:

• 2025 New Revised Senior Secondary Education Curriculum (SSEC)
• Relevant State Unified Scheme of Work
• Essential Chemistry for Senior Secondary Schools by Osei Yaw Ababio
• The HeadTeacher Scheme of work For The New Revised Senior Secondary Education Curriculum (SSEC)

Instructional Materials

The teacher will teach this lesson with the aid of:

• Periodic Table of elements.
• Charts showing the arrangement of electrons in atoms of common elements.
• Video simulation of the arrangement of electrons in atoms of different elements.
• CD or DVD players.
• Projector.
• Whiteboard and markers.
• Calculators.

Rationale for the Lesson

Understanding atomic structure is foundational to all of Chemistry, as it explains how elements behave and react. This lesson provides students with the tools to describe the arrangement of electrons in atoms and to distinguish between different atomic species. This knowledge is crucial for predicting chemical bonding, reactivity, and the properties of substances.

Prerequisite/Previous Knowledge

Students should have a basic understanding of atoms, subatomic particles (protons, neutrons, electrons), and the concept of elements from their Junior Secondary School science classes.

Lesson Content/Board Summary

Atomic Structure: Electronic Configuration Of The Atoms Of The First 20 Elements

Electronic Configuration

Electronic configuration refers to the distribution of electrons of an atom or molecule in atomic or molecular orbitals. Electrons occupy specific energy levels or shells around the nucleus. The shells are designated K, L, M, N, etc., starting from the innermost shell.

The maximum number of electrons that can occupy a shell is given by the formula (2n^2), where (n) is the shell number.

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

Electrons fill the lowest energy shells first before occupying higher energy shells. The outermost shell of an atom cannot hold more than 8 electrons, even if it is not completely filled according to the (2n^2) rule (octet rule).

Electronic Configuration of the First 20 Elements

The electronic configurations for the first 20 elements are:

1. Hydrogen (H, Z=1): 1
2. Helium (He, Z=2): 2
3. Lithium (Li, Z=3): 2, 1
4. Beryllium (Be, Z=4): 2, 2
5. Boron (B, Z=5): 2, 3
6. Carbon (C, Z=6): 2, 4
7. Nitrogen (N, Z=7): 2, 5
8. Oxygen (O, Z=8): 2, 6
9. Fluorine (F, Z=9): 2, 7
10. Neon (Ne, Z=10): 2, 8
11. Sodium (Na, Z=11): 2, 8, 1
12. Magnesium (Mg, Z=12): 2, 8, 2
13. Aluminium (Al, Z=13): 2, 8, 3
14. Silicon (Si, Z=14): 2, 8, 4
15. Phosphorus (P, Z=15): 2, 8, 5
16. Sulphur (S, Z=16): 2, 8, 6
17. Chlorine (Cl, Z=17): 2, 8, 7
18. Argon (Ar, Z=18): 2, 8, 8
19. Potassium (K, Z=19): 2, 8, 8, 1
20. Calcium (Ca, Z=20): 2, 8, 8, 2

Atomic Number (Z)

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

For example, Carbon (C) has an atomic number of 6, meaning every carbon atom 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 is also known as the nucleon number.

Mass Number (A) = Number of protons + Number of neutrons

For example, an atom of Oxygen with 8 protons and 8 neutrons has a mass number of 16 (8 + 8 = 16).

Isotopes

Isotopes are atoms of the same element that have the same atomic number (same number of protons) but different mass numbers (different numbers of neutrons). They have identical chemical properties but slightly different physical properties.

Examples of isotopes include:

1. Hydrogen isotopes:
   • Protium ((^{1}_{1}text{H})): 1 proton, 0 neutrons
   • Deuterium ((^{2}_{1}text{H})): 1 proton, 1 neutron
   • Tritium ((^{3}_{1}text{H})): 1 proton, 2 neutrons
2. Chlorine isotopes:
   • Chlorine-35 ((^{35}_{17}text{Cl})): 17 protons, 18 neutrons
   • Chlorine-37 ((^{37}_{17}text{Cl})): 17 protons, 20 neutrons

Relative Atomic Mass (RAM)

The relative atomic mass (RAM) of an element is the average mass of the atoms of the element compared to 1/12th the mass of a carbon-12 atom. Since most elements exist as a mixture of isotopes, the relative atomic mass is a weighted average of the masses of its naturally occurring isotopes, taking into account their relative abundances.

Formula for Relative Atomic Mass

[ text{RAM} = frac{(text{Mass of Isotope 1} times % text{Abundance 1}) + (text{Mass of Isotope 2} times % text{Abundance 2}) + dots}{100} ]

Example 1

Question: Naturally occurring chlorine consists of 75% Chlorine-35 and 25% Chlorine-37. Calculate the relative atomic mass of chlorine.

Solution:

Step 1: Write the formula.

[ text{RAM} = frac{(text{Mass of Isotope 1} times % text{Abundance 1}) + (text{Mass of Isotope 2} times % text{Abundance 2})}{100} ]

Step 2: Substitute the values.

[ text{RAM} = frac{(35 times 75) + (37 times 25)}{100} ]

Step 3: Simplify and write the answer.

[ text{RAM} = frac{2625 + 925}{100} = frac{3550}{100} = 35.5 ]

Answer: The relative atomic mass of chlorine is 35.5.

Teaching Methods/Instructional Techniques

Discussion, Explanation, Question and Answer, Guided Practice, Group Work, Demonstration, Video Simulation

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Recalling/Engaging

Teacher’s Activity: The teacher greets the students and reviews previous knowledge by asking questions like, “What are the basic particles that make up an atom?” and “What is the charge of a proton, neutron, and electron?” The teacher then introduces the topic: Electronic Configuration and Basic Atomic Terms.

Pupils’ Activity: Pupils respond to questions and listen attentively to the introduction of the new topic.

Learning Point: Review of atomic particles

Step 2: Exploring Atomic Number and Mass Number

Time: 10 minutes

Teaching Skill: Explanation/Questioning

Teacher’s Activity: The teacher explains the definitions of atomic number (Z) and mass number (A), using examples from the Periodic Table. The teacher guides students to identify these numbers for various elements.

Pupils’ Activity: Pupils listen, ask questions, and practice identifying atomic and mass numbers from the Periodic Table.

Learning Point: Atomic and mass numbers

Step 3: Understanding Isotopes

Time: 10 minutes

Teaching Skill: Explanation/Group Discussion

Teacher’s Activity: The teacher defines isotopes and explains their characteristics, providing examples like hydrogen and chlorine isotopes. The teacher then divides students into small groups to brainstorm and discuss the differences among atomic number, mass number, and isotopes.

Pupils’ Activity: Pupils listen to the explanation, participate in group discussions, and present their findings on the differences between the terms.

Learning Point: Concept of isotopes

Step 4: Calculating Relative Atomic Mass

Time: 10 minutes

Teaching Skill: Demonstration/Guided Practice

Teacher’s Activity: The teacher explains the concept of relative atomic mass and its calculation using isotopic abundances. The teacher demonstrates a worked example on the board, guiding students through each step of the calculation.

Pupils’ Activity: Pupils pay attention to the explanation and worked example, taking notes and asking clarifying questions.

Learning Point: Relative atomic mass calculation

Step 5: Practice with Relative Atomic Mass

Time: 5 minutes

Teaching Skill: Problem Solving/Individual Practice

Teacher’s Activity: The teacher provides another problem for students to solve individually or in pairs, calculating the relative atomic mass of an element given its isotopic data. The teacher moves around to provide support.

Pupils’ Activity: Pupils attempt to solve the calculation problem, applying the formula and steps learned.

Learning Point: Applying RAM formula

Step 6: Electronic Configuration of First 20 Elements

Time: 5 minutes

Teaching Skill: Explanation/Visualisation

Teacher’s Activity: The teacher explains the rules for electronic configuration (K, L, M, N shells) and uses charts or video simulations to show the electron arrangements for the first 20 elements. The teacher guides students to describe these configurations.

Pupils’ Activity: Pupils observe the charts/video, listen to explanations, and practice writing electronic configurations for different elements.

Learning Point: Electron arrangement in atoms

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

1. Differentiate between atomic number and mass number.
2. What are isotopes? Give one example.
3. Calculate the relative atomic mass of an element with two isotopes: Isotope A (mass 20, 90% abundance) and Isotope B (mass 22, 10% abundance).
4. Write the electronic configuration for Sodium (Na, Z=11).

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Understanding atomic concepts

Step 8: Note-Taking

Time: 10 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes on electronic configuration, atomic terms, and relative atomic mass calculation into their notebooks.

Pupils’ Activity: Pupils/students copy the notes carefully into their notebooks.

Learning Point: Recording lesson summary

Step 9: Conclusion

Time: 5 minutes

Teaching Skill: Summarising

Teacher’s Activity: The teacher briefly summarises the main points of the lesson, reinforcing the importance of electronic configuration and atomic terms in Chemistry. The teacher encourages students to review their notes.

Pupils’ Activity: Pupils listen to the summary and prepare for the next lesson.

Learning Point: Consolidation of key concepts

Continuous Assessment/Further Study

Type: Homework

Instruction: Answer the following questions in your Chemistry notebook.

1. Define the terms: atomic number, mass number, and isotopes.
2. An element X has two isotopes: (^{63}text{X}) (69.1% abundance) and (^{65}text{X}) (30.9% abundance). Calculate the relative atomic mass of element X.
3. Write the electronic configuration for the following elements:
   1. Calcium (Ca, Z=20)
   2. Oxygen (O, Z=8)
   3. Aluminium (Al, Z=13)

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 the same atomic number but different mass numbers.
• Electronic Configuration – The arrangement of electrons in the shells or orbitals of an atom.
• Relative Atomic Mass – The weighted average mass of an element’s isotopes compared to 1/12th the mass of a carbon-12 atom.

Differentiation

For students who grasp concepts quickly, provide additional problems involving elements with more complex isotopic data or ask them to research the applications of isotopes. For students needing more support, provide simplified diagrams of electron shells and offer one-on-one guidance during calculations, focusing on basic definitions and the first few elements.

Suggested Lesson Videos

YouTube search for “electronic configuration first 20 elements ss1 chemistry”
YouTube search for “atomic number mass number isotopes relative atomic mass ss1”