Changes of state and Postulates of Dalton’s atomic theory for SS 1

Class: SS 1
Term: Second Term
Week: 4
Age: 15 years
Duration: 60 minutes
Subject: Chemistry
Curriculum Theme: The Chemical World
Focal competence: Identifying the fundamental particles of matter
Key competencies/values: C Collaborations
Skills:

• Recording through drawing of apparatus set-up, and making short notes of the activities performed to change matter from one state to another
• Handling (i.e. setting up) of apparatus to demonstrate change of state

Previous Lesson: Matter, Solid, Liquid, Gas and Plasma States
Topic: Particulate Nature Of Matter: Changes Of State
Subject Matter: Changes of state, Postulates of Dalton’s atomic theory

Specific Objectives

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

Cognitive Domain

• State the postulates of Dalton’s Atomic theory.
• Explain the significance of Dalton’s theory in chemistry.
• Identify everything in the environment as matter.
• Distinguish between solid, liquid and gaseous matter in terms of Dalton’s atomic theory.

Affective Domain

• Appreciate the importance of Dalton’s atomic theory in understanding matter.
• Collaborate effectively in group discussions and experimental activities.

Psychomotor Domain

• Draw simple apparatus set-ups for demonstrating changes of state.
• Set up simple apparatus to demonstrate changes of state.
• Perform simple experiments to observe changes of state.

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
• A suitable Chemistry textbook for SS 1
• 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:

• Charts showing states of matter and changes of state
• Diagrams illustrating Dalton’s atomic theory
• Model kits representing atoms and molecules
• Pictures or videos demonstrating changes of state
• Beakers, tripod stand, gauze, Bunsen burner/spirit lamp, ice cubes, water, watch glass, iodine crystals (for sublimation)

Rationale for the Lesson

This lesson is important for understanding the fundamental nature of matter and how it behaves under different conditions. It provides a foundational understanding of the particulate nature of matter and introduces Dalton’s atomic theory, which is crucial for subsequent topics in chemistry. Students will gain practical skills in observing and explaining everyday phenomena related to changes in matter.

Prerequisite/Previous Knowledge

Students should have a basic understanding of what matter is and its general classification into solids, liquids, and gases from their Junior Secondary School science lessons.

Lesson Content/Board Summary

Particulate Nature Of Matter: Changes Of State

Changes of State

Matter can exist in different physical states: solid, liquid, and gas. These states can be interconverted by changing temperature or pressure. The processes involved are:

1. Melting: The process by which a solid changes into a liquid upon heating. For example, ice melting into water.
2. Boiling: The process by which a liquid changes into a gas (vapour) rapidly throughout the bulk of the liquid at a specific temperature called the boiling point. For example, water boiling to form steam.
3. Condensation: The process by which a gas changes into a liquid upon cooling. For example, steam turning back into water droplets on a cold surface.
4. Freezing: The process by which a liquid changes into a solid upon cooling. For example, water freezing into ice.
5. Sublimation: The process by which a solid changes directly into a gas without passing through the liquid state, and vice-versa. For example, solid iodine or naphthalene balls subliming.

Postulates of Dalton’s Atomic Theory

John Dalton proposed his atomic theory in 1808, which laid the foundation for modern chemistry. His main postulates are:

1. All matter is composed of extremely small, indivisible particles called atoms.
2. Atoms of a given element are identical in size, mass, and other properties. Atoms of different elements differ in size, mass, and other properties.
3. Atoms cannot be created or destroyed in a chemical reaction. They are merely rearranged.
4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
5. In a given compound, the relative number and types of atoms are constant.

Significance of Dalton’s Atomic Theory in Chemistry

Dalton’s atomic theory was significant because it:

1. Provided a scientific basis for the concept of atoms, moving it from philosophical speculation to a testable hypothesis.
2. Explained the Law of Conservation of Mass (atoms are not created or destroyed).
3. Explained the Law of Definite Proportions (atoms combine in fixed ratios).
4. Explained the Law of Multiple Proportions (elements can combine in different whole-number ratios to form different compounds).
5. Paved the way for future developments in atomic structure and chemical bonding.

Distinguishing States of Matter in Terms of Dalton’s Atomic Theory

Based on Dalton’s idea of atoms as fundamental particles, the states of matter can be distinguished by the arrangement and movement of these particles:

1. Solids:
   • Atoms are closely packed in fixed positions.
   • Strong forces of attraction hold the atoms together.
   • Atoms vibrate about their fixed positions but do not move freely.
   • Solids have a definite shape and a definite volume.
2. Liquids:
   • Atoms are closely packed but are not in fixed positions.
   • Weaker forces of attraction allow atoms to slide past one another.
   • Atoms can move freely within the bulk of the liquid.
   • Liquids have a definite volume but take the shape of their container.
3. Gases:
   • Atoms are far apart from each other.
   • Very weak or negligible forces of attraction between atoms.
   • Atoms move randomly and rapidly in all directions.
   • Gases have no definite shape or volume and fill their container.

Teaching Methods/Instructional Techniques

Discussion, Demonstration, Guided Practice, Question and Answer, Explanation, Observation, Group Work, Practical Activity

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Recalling/Engaging

Teacher’s Activity: The teacher greets the students and asks them to recall what they know about matter and its states from JSS science. The teacher then introduces the topic, “Particulate Nature Of Matter: Changes Of State,” and links it to everyday observations.

Pupils’ Activity: Pupils respond to questions about matter and its states, sharing their prior knowledge.

Learning Point: Matter and its states

Step 2: Changes of State

Time: 10 minutes

Teaching Skill: Explanation/Illustration

Teacher’s Activity: The teacher explains the different changes of state (melting, boiling, condensation, freezing, sublimation) with simple examples. The teacher uses charts and diagrams to illustrate these processes and clarifies related chemical terms and observable properties.

Pupils’ Activity: Pupils listen attentively, ask questions for clarification, and observe the charts.

Learning Point: Types of state changes

Step 3: Demonstration of Changes of State

Time: 15 minutes

Teaching Skill: Demonstration/Guidance

Teacher’s Activity: The teacher guides students in groups to perform simple experiments to demonstrate changes of state, e.g., melting ice, boiling water, condensation on a cold surface, or sublimation of iodine. The teacher ensures safety and guides students to record observations and draw apparatus set-ups.

Pupils’ Activity: Pupils work in groups, set up apparatus, perform experiments, observe changes, and record their findings and drawings in their notebooks.

Learning Point: Practical state changes

Step 4: Postulates of Dalton’s Atomic Theory

Time: 10 minutes

Teaching Skill: Explanation/Discussion

Teacher’s Activity: The teacher introduces Dalton’s atomic theory, explaining each postulate clearly. The teacher uses diagrams or model kits to help students visualize the concepts of atoms and their combinations.

Pupils’ Activity: Pupils listen, take notes, and participate in discussions about the postulates.

Learning Point: Dalton’s atomic postulates

Step 5: Significance of Dalton’s Theory

Time: 5 minutes

Teaching Skill: Elaboration/Connection

Teacher’s Activity: The teacher explains the significance of Dalton’s atomic theory in the development of chemistry, linking it to fundamental laws like the Law of Conservation of Mass and Law of Definite Proportions.

Pupils’ Activity: Pupils listen and contribute to the discussion on the importance of the theory.

Learning Point: Importance of Dalton’s theory

Step 6: States of Matter and Dalton’s Theory

Time: 5 minutes

Teaching Skill: Comparison/Application

Teacher’s Activity: The teacher guides students to distinguish between solid, liquid, and gaseous matter using the principles of Dalton’s atomic theory, focusing on particle arrangement, forces, and movement.

Pupils’ Activity: Pupils discuss and explain the differences between the states of matter based on atomic arrangement.

Learning Point: States of matter distinction

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. State any three postulates of Dalton’s Atomic theory.
2. Explain the significance of Dalton’s theory in understanding chemical reactions.
3. How would you distinguish between a solid and a liquid based on Dalton’s atomic theory?
4. Name two processes by which a liquid can change into a gas.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Understanding changes of state

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 changes of state and Dalton’s atomic theory into their notebooks.

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

Learning Point: Recording lesson notes

Step 9: Conclusion

Time: 5 minutes

Teaching Skill: Consolidation

Teacher’s Activity: The teacher briefly summarizes the key points of the lesson, emphasizing the particulate nature of matter and the foundational role of Dalton’s theory. The teacher encourages students to observe changes of state in their daily lives.

Pupils’ Activity: Pupils listen and reflect on the lesson’s main concepts.

Learning Point: Lesson summary reinforcement

Continuous Assessment/Further Study

Type: Homework

Instruction: Answer the following questions in your Chemistry notebook:

1. Describe an experiment you could perform at home to demonstrate the process of freezing.
2. List all five postulates of Dalton’s Atomic Theory.
3. Explain how the kinetic theory of matter relates to the changes of state discussed in class.
4. Research and write a short paragraph on one limitation of Dalton’s atomic theory.

Lesson Keywords

• Matter – Anything that has mass and occupies space.
• Solid – State of matter with definite shape and volume, particles closely packed.
• Liquid – State of matter with definite volume but no definite shape, particles can slide past each other.
• Gas – State of matter with no definite shape or volume, particles are far apart and move randomly.
• Melting – Solid to liquid.
• Boiling – Liquid to gas.
• Condensation – Gas to liquid.
• Freezing – Liquid to solid.
• Sublimation – Solid directly to gas or gas directly to solid.
• Atom – The smallest indivisible particle of an element (according to Dalton).
• Postulate – A statement accepted as true without proof as a basis for argument.

Differentiation

For struggling learners: Provide simplified diagrams and models. Offer one-on-one guidance during practical activities and simplify the language used for explanations. Focus on identifying and defining the basic changes of state and the first two postulates of Dalton’s theory.

For advanced learners: Encourage them to research the modern modifications to Dalton’s atomic theory. Challenge them to explain the energy changes involved in each change of state and to design an experiment to measure a boiling point.

Suggested Lesson Videos

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