Lesson Note on Periodic Table: Trends, Diagonal Relationship and Ionization Energy for SSS 2

Class: Senior Secondary School 2 (SS2 / SSS2)
Term: First Term
Week: 3
Age: 16 years
Duration: 45 minutes
Subject: Chemistry
Curriculum Theme: Periodic Chemistry
Previous Lesson: Periodic Table: Meaning, Periodic Law, Blocks and Families.
Topic: PERIODIC TABLE
Subject Matter: Properties (changes in sizes down the group and across periods, accompanying changes in properties), diagonal relationships, ionization energy and electron affinity (changes down the group and across the period)

Specific Objectives

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

Cognitive Domain:

• Describe trends in atomic and ionic sizes across periods and down groups.
• State changes in ionization energy and electron affinity down groups and across periods.
• Explain diagonal relationships with relevant examples.

Affective Domain:

• Appreciate the systematic arrangement of elements in the periodic table.
• Develop an interest in understanding the chemical properties of elements.

Psychomotor Domain:

• Draw simple diagrams illustrating trends in atomic properties.
• Identify elements that exhibit diagonal relationships on a periodic table chart.

Social Domain:

• Participate actively in class discussions about periodic trends.
• Collaborate with peers to understand complex concepts related to the periodic table.

Reference Materials

The following resources were used in planning this lesson:

• Senior Secondary Schools Education Curriculum
• State Unified Scheme of Work
• New School Chemistry for Senior Secondary Schools by Osei Yaw Ababio

Instructional Materials

The teacher will teach this lesson with the aid of:

• Sodium metal
• Magnesium ribbon
• Aluminum metal
• Heat source
• Water
• Glass trough
• Beakers
• A large Periodic Table chart

Rationale for the Lesson

This lesson helps pupils understand how the properties of elements change in a predictable way across the periodic table. This knowledge is important for predicting chemical behavior and understanding why elements react the way they do in various chemical processes.

Prerequisite/Previous Knowledge

Pupils are expected to have prior knowledge of the structure of the periodic table, including groups, periods, and the general classification of elements (metals, non-metals, metalloids).

Lesson Content/Board Summary

The Periodic Table: Trends and Relationships

1. Atomic and Ionic Radii

Atomic radius is defined as half the distance between the nuclei of two identical atoms joined by a single covalent bond. Ionic radius is the radius of an ion.

• Across a Period (from left to right): Atomic and ionic radii generally decrease. This is due to an increase in nuclear charge (number of protons) which pulls the electrons closer to the nucleus, while the number of electron shells remains the same.
• Down a Group (from top to bottom): Atomic and ionic radii generally increase. This is because new electron shells are added with each successive element, increasing the distance of the outermost electrons from the nucleus, despite an increase in nuclear charge.

2. Ionization Energy

Ionization energy (IE) is the minimum energy required to remove one mole of electrons from one mole of gaseous atoms in their ground state to form one mole of gaseous ions.

• Across a Period (from left to right): Ionization energy generally increases. This is due to an increase in nuclear charge and a decrease in atomic size, making it harder to remove electrons.
• Down a Group (from top to bottom): Ionization energy generally decreases. This is because atomic size increases and the outermost electrons are further from the nucleus and experience more shielding from inner electrons, making them easier to remove.

3. Electron Affinity

Electron affinity is the energy change that occurs when one mole of electrons is added to one mole of gaseous atoms in their ground state to form one mole of gaseous negative ions.

• Across a Period (from left to right): Electron affinity generally increases (becomes more negative/exothermic). This is due to increasing nuclear charge and decreasing atomic size, making the atom more attractive to incoming electrons. Halogens have very high electron affinities.
• Down a Group (from top to bottom): Electron affinity generally decreases (becomes less negative/exothermic). This is because of increasing atomic size and increased shielding, which reduces the attraction for an added electron.

4. Diagonal Relationships

Diagonal relationships refer to similarities in chemical properties between certain pairs of diagonally adjacent elements in the second and third periods of the periodic table. These similarities are often attributed to similar charge/radius ratios of their ions.

Examples of diagonal relationships include:

• Lithium (Li) and Magnesium (Mg): Both form nitrides (Li₃N, Mg₃N₂), react with oxygen to form normal oxides (Li₂O, MgO), and their hydroxides are weak bases.
• Beryllium (Be) and Aluminum (Al): Both are amphoteric (react with acids and bases), form covalent compounds, and their halides are dimeric.
• Boron (B) and Silicon (Si): Both are metalloids, form acidic oxides, and their hydrides are volatile.

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 their previous knowledge of the periodic table by asking them to identify groups and periods. The teacher then introduces the topic of periodic properties.
Pupils’ Activity: Pupils respond to the teacher’s questions and listen attentively to the introduction.
Learning Point: Pupils recall basic knowledge of the periodic table and are prepared for the new topic.

Step 2: Atomic and Ionic Radii

Time: 8 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher explains the definitions of atomic and ionic radii and uses a periodic table chart to illustrate the trends across periods and down groups, providing reasons for these trends.
Pupils’ Activity: Pupils observe the chart, take notes, and describe the trends in atomic and ionic sizes.
Learning Point: Pupils understand the definitions and trends of atomic and ionic radii.

Step 3: Ionization Energy

Time: 8 minutes
Teaching Skill: Explanation/Questioning
Teacher’s Activity: The teacher defines ionization energy and explains how it changes across periods and down groups, linking it to atomic size and nuclear charge. The teacher asks questions to check understanding.
Pupils’ Activity: Pupils listen, ask questions for clarification, and state the changes in ionization energy.
Learning Point: Pupils understand the concept of ionization energy and its periodic trends.

Step 4: Electron Affinity

Time: 8 minutes
Teaching Skill: Explanation/Comparison
Teacher’s Activity: The teacher defines electron affinity and explains its trends across periods and down groups, comparing it with ionization energy where relevant. The teacher uses examples to clarify the concept.
Pupils’ Activity: Pupils pay attention, compare the trend with ionization energy, and state the changes in electron affinity.
Learning Point: Pupils grasp the definition and periodic trends of electron affinity.

Step 5: Diagonal Relationships

Time: 8 minutes
Teaching Skill: Elucidation/Examples
Teacher’s Activity: The teacher explains the concept of diagonal relationships and provides specific examples (Li-Mg, Be-Al, B-Si) with their similar properties. The teacher points out these pairs on the periodic table chart.
Pupils’ Activity: Pupils listen, take notes on the examples, and explain diagonal relationships.
Learning Point: Pupils understand what diagonal relationships are and can provide examples.

Step 6: Class Activity/Discussion

Time: 3 minutes
Teaching Skill: Group Discussion
Teacher’s Activity: The teacher facilitates a brief discussion asking pupils to summarize one trend they found most interesting or challenging.
Pupils’ Activity: Pupils share their thoughts and clarify any remaining doubts.
Learning Point: Pupils engage in active learning and consolidate their understanding.

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. Define atomic radius and ionization energy.
2. How does atomic radius change across a period and down a group?
3. State the general trend of electron affinity across a period.
4. Explain what is meant by diagonal relationship, giving one example.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teacher’s Activity: The teacher summarizes the key periodic trends discussed and assigns homework, asking pupils to research other periodic properties like electronegativity and metallic character.
Pupils’ Activity: Pupils listen to the summary and copy down the homework assignment.
Learning Point: Pupils recap the lesson and are prepared for future related topics.

Lesson Keywords

• Atomic Radius – Half the distance between the nuclei of two identical atoms.
• Ionic Radius – The radius of an ion.
• Ionization Energy – Energy to remove an electron from a gaseous atom.
• Electron Affinity – Energy change when an electron is added to a gaseous atom.
• Diagonal Relationship – Similarities in properties between diagonally adjacent elements.

Differentiation

For struggling learners, the teacher will provide simplified diagrams and focus on one trend at a time with repeated examples. Advanced learners will be encouraged to explore exceptions to the general trends and relate these properties to real-world applications of elements.

Note for teachers using this lesson plan

Teachers should ensure the periodic table chart is clearly visible and used frequently during explanations. Encourage pupils to draw simplified representations of trends in their notebooks. Practical demonstrations (like reaction of Na, Mg, Al with water/heat, if facilities permit) can enhance understanding of property changes.