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Science lesson plan · 8th grade (Year 9 in England) · 60 minutes

Group 7: the halogens and displacement

Atoms, elements and the periodic table

CCSS NGSS.HS-PS1-1CCSS NGSS.HS-PS1-2England: GCSE Combined Science: Atomic structure and the periodic table (group 7)

Objective and success criteria

Students will: Group 7: the halogens and displacement.

  • I can answer questions on today's skill on my own, without help.
  • I can explain each step and say why it works.
  • I can check my answer and spot a mistake.

Before and after

Needs first: The periodic table: groups and periods

Leads to: the next skill in this area.

Materials: Periodic tables, Atom model kits, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).

Warm-up · 6 min

  • Quick retrieval from earlier learning (The periodic table: groups and periods). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. Which family does sodium belong to? (alkali metals (group 1) / halogens (group 17, also called group 7) / noble gases (group 18, also called group 0)) → alkali metals (group 1)Prompt: Is it a soft metal, a coloured reactive non-metal, or an unreactive gas?
  2. Which family does bromine belong to? (alkali metals (group 1) / halogens (group 17, also called group 7) / noble gases (group 18, also called group 0)) → halogens (group 17, also called group 7)Prompt: Is it a soft metal, a coloured reactive non-metal, or an unreactive gas?
  3. Which family does iodine belong to? (alkali metals (group 1) / halogens (group 17, also called group 7) / noble gases (group 18, also called group 0)) → halogens (group 17, also called group 7)Prompt: Is it a soft metal, a coloured reactive non-metal, or an unreactive gas?

Hook · 6 min

  • Show the periodic table and ask what patterns students can see before anything is explained.
  • Share the objective: Group 7: the halogens and displacement. Read the success criteria together.

I do: model it · 12 min

  • Work through the example out loud, saying why you do each step, not just what you do.
  • Example: Chlorine water is added to potassium iodide solution. Will a reaction happen?
  • Step 1: chlorine is above iodine, so it is more reactive.
  • Step 2: So the answer is: yes: chlorine displaces iodine
  • Answer: yes: chlorine displaces iodine
  • Pause after each step and ask a student to say what comes next.

We do: guided practice · 12 min

  • Do these together. Students try each step on whiteboards before you reveal it.
  • Use the hints as prompts rather than giving the answer.
  1. Chlorine water is added to potassium iodide solution. Will a reaction happen? (yes: chlorine displaces iodine / no reaction) → yes: chlorine displaces iodinePrompt: A more reactive halogen displaces a less reactive one from its compound.
  2. Why is chlorine added to drinking water and swimming pools? (to kill microorganisms / to make the water blue / to add minerals / to make it fizzy) → to kill microorganismsPrompt: Chlorine is toxic to microbes at low concentrations.

You do: independent practice · 17 min

  • Students work on the student sheet. Circulate and check the first two answers of every student early.
  • Students who finish: write a question of their own for a partner, with the answer.

The 8 questions are on the student sheet below, with answers in the key.

Exit ticket · 7 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. Iodine water is added to potassium bromide solution. Will a reaction happen? (yes: iodine displaces bromine / no reaction) → no reactionPrompt: A more reactive halogen displaces a less reactive one from its compound.
  2. Why does reactivity decrease down group 7? (The atoms have fewer outer electrons / The outer shell is further from the nucleus, so gaining an electron is harder / The atoms lose electrons more easily / Halogens are metals) → The outer shell is further from the nucleus, so gaining an electron is harderPrompt: Halogens react by gaining one electron.

Watch out for

  • Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
  • Remembering facts without the reason: ask "why?" and "what is the evidence?"

Support and stretch

Support

  • Review first: The periodic table: groups and periods.
  • Use concrete materials: periodic tables.
  • Give the first step of each question, or a partly worked example to finish.
  • Pair with a confident partner for the guided practice.

Stretch

  • Explain a common mistake in writing and how to fix it.
  • Write a word problem that uses today's skill, then solve a partner's.

Homework and more practice

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-8.

Free lesson plan from eurekami.com/lesson-plan-builder

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Group 7: the halogens and displacement

Name

Date

Score/ 8

  1. Question 1

    Why is chlorine added to drinking water and swimming pools?

    • A. to add minerals
    • B. to make the water blue
    • C. to make it fizzy
    • D. to kill microorganisms

  2. Question 2

    The halogens: which statement is true?

    • A. Halogens are found as single atoms.
    • B. Boiling points of halogens decrease down the group.
    • C. Iodine is more reactive than chlorine.
    • D. Halogens have seven electrons in their outer shell.

  3. Question 3

    Chlorine water is added to potassium bromide solution. Will a reaction happen?

    • A. yes: chlorine displaces bromine
    • B. no reaction

  4. Question 4

    Why does reactivity decrease down group 7?

    • A. The atoms have fewer outer electrons
    • B. The atoms lose electrons more easily
    • C. The outer shell is further from the nucleus, so gaining an electron is harder
    • D. Halogens are metals

  5. Question 5

    Iodine water is added to potassium bromide solution. Will a reaction happen?

    • A. yes: iodine displaces bromine
    • B. no reaction

  6. Question 6

    Bromine water is added to potassium iodide solution. Will a reaction happen?

    • A. yes: bromine displaces iodine
    • B. no reaction

  7. Question 7

    Halogens exist as molecules. What is the formula of a chlorine molecule?

    • A. Cl
    • B. Cl₂
    • C. Cl₃
    • D. Cl⁻

  8. Question 8

    Iodine water is added to potassium chloride solution. Will a reaction happen?

    • A. yes: iodine displaces chlorine
    • B. no reaction

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Answer key: Group 7: the halogens and displacement

  1. 1. D. to kill microorganisms

  2. 2. D. Halogens have seven electrons in their outer shell.

  3. 3. A. yes: chlorine displaces bromine

  4. 4. C. The outer shell is further from the nucleus, so gaining an electron is harder

  5. 5. B. no reaction

  6. 6. A. yes: bromine displaces iodine

  7. 7. B. Cl₂

  8. 8. B. no reaction