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2bInorganic Chemistry

Group 7 (halogens) – chlorine, bromine and iodine — Edexcel Linear - OL (Chemistry) Revision Notes & Topical Questions

5 min read 7 parts Lesson 2 of 23 1 quiz

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Lesson summary

Group 7 (halogens) Edexcel O Level Linear Chemistry notes: know the colours, physical states (at room temperature) and trends in physical properties of these elementsVolatility decreases down the group (stronger id–id forces).Reducing power of halide ions increases down the group…

  • Group 7 (halogens) Edexcel O Level Linear Chemistry: what to do next
  • Displacement
  • Disproportionation
  • Oxidising power
  • Hydrogen halides
  • Silver nitrate test

Part 1 of 6Key ideas

Key ideas
Volatility decreases down the group (stronger id–id forces).
Reducing power of halide ions increases down the group.
H–X bond strength decreases down, so HI decomposes most easily.

Part 2 of 6Syllabus points

Syllabus points
know the colours, physical states (at room temperature) and trends in physical properties of these elements
use knowledge of trends in Group 7 to predict the properties of other halogens
understand how displacement reactions involving halogens and halides provide evidence for the trend in reactivity in Group 7 2.8C explain the trend in reactivity in Group 7 in terms of electronic configurations

Part 3 of 6Process & sequence

1
Acidify halide solution with dilute HNO₃.
2
Add AgNO₃(aq).
3
Note colour of precipitate.
4
Add ammonia to confirm.
Reactions
Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂
Cl₂ + H₂O ⇌ HCl + HClO
Cl₂ + 2NaOH (cold) → NaCl + NaClO + H₂O
3Cl₂ + 6NaOH (hot) → 5NaCl + NaClO₃ + 3H₂O
  • Conc H₂SO₄ + NaCl
  • HCl only
  • + NaBr
  • HBr, Br₂, SO₂
  • + NaI
  • HI, I₂, SO₂, S, H₂S

Part 4 of 6Summary

Summary
Oxidising power of halogens decreases down the group.
AgBr is a cream precipitate.

Part 5 of 6Keep going

Group 7 (halogens) Edexcel O Level Linear Chemistry: what to do next

These Group 7 (halogens) Edexcel O Level Linear Chemistry notes covered the key ideas, worked examples and exam technique for this topic. Check your Group 7 (halogens) Edexcel O Level Linear Chemistry understanding with the practice questions below, then reread any Group 7 (halogens) Edexcel O Level Linear Chemistry point you were unsure about before moving on.

1
Practice: Group 7 (halogens) Edexcel O Level Linear Chemistry practice questions
2
Previous lesson: 2a Group 1 (alkali metals) - lithium, sodium and potassium — Notes
3
Next lesson: 2c Gases in the atmosphere — Notes
4
Course: Edexcel Linear – OL (chemistry) — all units
5
Official syllabus: Pearson Edexcel International GCSEs

Group 7 (halogens) Edexcel O Level Linear Chemistry revision notes

Part 6 of 6Compare: Compare

Halogens and halide tests
HalogenState/colourColour in hexaneHalide + AgNO₃Precipitate + dilute NH₃+ conc NH₃
FluorinePale yellow gas—No precipitate——
ChlorineGreen-yellow gasPale greenWhite AgClDissolvesDissolves
BromineRed-brown liquidOrangeCream AgBrInsolubleDissolves
IodineGrey-black solidViolet / purpleYellow AgIInsolubleInsoluble

Key terms

Command terms

Command terms
Give / State / Name
Recall a fact; one idea per mark.
Define
Give the exact meaning using the specification keywords.
Describe
Give an account of what happens / the pattern in data, quoting values; no reasons needed.
Explain
Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.
Suggest
Use knowledge in a new context; more than one answer may be accepted.
Compare
Similarities and differences; each point must refer to both items.
Calculate
Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.
Discuss
Explore the issue from different angles and link the points.
Evaluate / Assess
Weigh strengths and weaknesses and reach a supported judgement.
Deduce
Draw a conclusion from the information given.
Justify
Support a statement/choice with evidence.

Exam technique

Keywords the mark scheme looks for in this lesson

Keywords the mark scheme looks for in this lesson
Halogens · Displacement · Disproportionation · Oxidising power · Hydrogen halides · Silver nitrate test · Bleach · Chlorination of water
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.

How to get full marks (examiner guidance)

How to get full marks (examiner guidance)
Use specification keywords exactly (e.g. electronegativity, nucleophile, dynamic equilibrium, activation energy).
Link ideas
Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.
Use the information in the question
“discuss/evaluate” answers must use the data provided and match the number of marks.
Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.
Avoid vague words
“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.
Do not extrapolate a graph line beyond the data or to zero unless asked.
Six-mark extended responses are marked on content AND a logical, linked line of reasoning.

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