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Group 7(17), the halogens
This topic develops redox and periodic-trend reasoning for halogens and halide ions.
8
Objectives
40
Flashcards
36
Questions
90 min
Study time
AQAA LevelChemistryInorganic chemistry
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Syllabus checklist
What you need to know
8 objective pages available
Halogen trends and displacement4 objectives
- Describe trends in electronegativity and boiling point down Group 7.
- Explain the trend in oxidising ability of halogens.
- Predict and explain halogen displacement reactions.
- Write ionic equations for halogen displacement reactions.
Halide ions and uses of chlorine4 objectives
- Describe tests for halide ions using silver nitrate and ammonia.
- Explain the use of chlorine in water treatment.
- Explain disproportionation reactions of chlorine in water and alkali.
- Evaluate benefits and risks of chlorine use.
Key terms
ElectronegativityBoiling Pointoxidising abilityhalogenshalogen displacement reactionionic equationHalide ion testSilver nitrate reactionchlorinewater treatmentdisproportionation reactionchlorine in water treatment
Exam tips
- Understanding Electronegativity Trends: Explain clearly by remember that electronegativity decreases down Group 7 due to increased atomic radius and shielding effect. This means that halogens become less effective at attracting electrons as you move down the group. Link the point to Halogen trends and displacement, then state the evidence, calculation, mechanism, observation, or conclusion required by the question.
- Understanding Halogen Oxidising Ability: Remember that the oxidising ability of halogens increases as you move up Group 7. This is because smaller atoms have a stronger attraction for electrons.
Common mistakes
- Electronegativity Misunderstanding: Remember that electronegativity decreases down Group 7 due to increased atomic size and shielding effect. For example, fluorine is the most electronegative element, while iodine is less electronegative. This is because as you go down the group, the number of electron shells increases, which reduces the nucleus's pull on the bonding electrons.
- Oxidising Ability Confusion: To clarify, remember that oxidising ability increases up the group, while reactivity increases down the group. For example, fluorine is the most reactive but not the strongest oxidising agent compared to chlorine. Focus on the definition of oxidising ability as the tendency to gain electrons.
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