SHS2 Chemistry · Semester 2 Week 7: Periodicity

Lesson notes

Learning Objectives

Indicator: 2.2.1.LI.1 - Explain the physical and chemical properties of the halogens (Group 17 elements).

By the end of the lesson, learners can:

Describe the physical state, colour, melting point, boiling point and bond energy trends for fluorine, chlorine, bromine and iodine, and explain the reasons for these trends in terms of molecular size and intermolecular forces.
Identify the anomaly in the bond energies of the halogens (fluorine’s bond being weaker than expected) and explain it using the concept of lone pair repulsion between small atoms.
Write the electron configurations of the halogens and predict their oxidation states, explaining why fluorine is restricted to the -1 state while other halogens show variable positive oxidation states.
Explain the trend in reactivity of the halogens using standard electrode potential data, and predict the products of displacement reactions and precipitation reactions involving halide ions.
Write balanced chemical equations for the reactions of halogens with water, alkalis and halide ions, and relate these reactions to everyday uses such as water treatment and bleaching.

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Curriculum details

Strand: Systematic Chemistry of the Elements (Strand 2)
Sub-strand: Periodicity (2.1)
Content standard: 2.2.1.CS.2 - Demonstrate knowledge and understanding of the pattern of the physical and chemical properties of the halogens as well as their uses. 2.2.1.LO.1 Predict and describe the trends of chemical and physical properties of elements and their compounds in the periodic table. 2.2.1.LO.2 Predict and describe the physical and chemical properties of the halogens as well as their uses in everyday life.
Indicator: 2.2.1.LI.1 - Explain the physical and chemical properties of the halogens (Group 17 elements).
Suggested placement: Semester 2, Week 7 (Week 27 of the year)
Our suggestion, laid out in curriculum order across three terms of twelve weeks. NaCCA does not fix the week, so follow your school's scheme of learning.
Curriculum reference: NaCCA curriculum document, p. 78

Exemplars (from the NaCCA curriculum)

Talk for Learning Approach:
- In mixed-ability groups, discuss the variations in the physical properties of the halogens under the following headings: a. Physical State b. Melting and Boiling points c. Bond energies
- Discuss any anomalies in the bond energies.
Collaborative Learning:
- In mixed-ability groups, discuss the electron configurations and the exhibition of variable oxidation states of the halogens.
- Discuss the similarities in chemical nature of the halogens.
- Deduce the differences in the reactivity of the halogens based on their standard electrode potential values.
- Use the following reactions for your discussions: a. Halogens with halide ions (displacement reactions). b. Halide ions with silver ions (precipitation reactions).
Digital Learning:
- In mixed-ability groups, watch videos and discuss the reagents, conditions and products formed when the halogens react with water and alkalis.
- Write balanced chemical equations to show how the reactions occur.
Teaching and Learning Materials:
- * Periodic table showing atomic numbers, electron configuration of the elements as well as their fixed or variable oxidation states * ICT tools * KOH * NaOH
- * Worksheets * Bleach solution
- Water * A piece of stained cloth
Assessment (2.2.1.AS.1). The document marks these depth-of-knowledge levels for this indicator: Level 3 Strategic reasoning.