SHS2 Chemistry · Semester 2 Week 8: Periodicity

Lesson notes

Learning Objectives

Indicator: 2.2.1.LI.2 - Describe the reaction of halide salts and explain the differences in acid strength of the hydrogen halides as well as the uses of the halogens.

By the end of the lesson, learners can:

Predict and explain the relative reducing power of the halide ions (Cl⁻, Br⁻, I⁻) using their position in Group 17 and their electron configurations.
Write and balance chemical equations for the reactions of solid halide salts with concentrated tetraoxosulphate (VI) acid, including the distinctive test for chloride, bromide and iodide salts.
Explain the trend in acid strength of the hydrogen halides (HF, HCl, HBr, HI) in terms of bond dissociation energies and Ka values.
Describe the chemical basis for at least four everyday uses of halogens, including water purification, bleaching, disinfection and halogenated hydrocarbons.
Apply the reducing power trend to predict the outcome of displacement reactions between halogens and halide salts.

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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.2 - Describe the reaction of halide salts and explain the differences in acid strength of the hydrogen halides as well as the uses of the halogens.
Suggested placement: Semester 2, Week 8 (Week 28 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: Using think-pair-share approach,
- Explain the differences in reducing power of the halides.
- Write chemical equations to illustrate the various reactions of halides salts with concentrated tetraoxosulphate (VI) acid.
Collaborative Learning: In mixed-ability groups:
- Discuss the acid strengths of hydrogen halides under the following headings: a. Relative bond strengths of HX, where X is F, Cl, Br and I. b. Ka values of HX
- Discuss the thermal stability of the halogen halides in terms of their bond energies.
- Explain the chemical basis for the uses of the reactions of halogens in everyday life under the following headings: a. Purification of water for drinking b. The use bleach to oxidise dyes and other coloured molecules c. Disinfecting toilets d. Use of halogenated hydrocarbons as solvents, refrigerants and in aerosols
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.2). The document marks these depth-of-knowledge levels for this indicator: Level 2 Skills of conceptual understanding.