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Science lesson plan · 8th grade (Year 9 in England) · 30 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 · 4 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 fluorine 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?
  2. Which family does neon belong to? (alkali metals (group 1) / halogens (group 17, also called group 7) / noble gases (group 18, also called group 0)) → noble gases (group 18, also called group 0)Prompt: Is it a soft metal, a coloured reactive non-metal, or an unreactive gas?
  3. Which family does lithium 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?

Hook · 3 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 · 7 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 · 6 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. Bromine water is added to potassium iodide solution. Will a reaction happen? (yes: bromine displaces iodine / no reaction) → yes: bromine 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 add minerals / to make the water blue / to kill microorganisms / to make it fizzy) → to kill microorganismsPrompt: Chlorine is toxic to microbes at low concentrations.

You do: independent practice · 7 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 6 questions are on the student sheet below, with answers in the key.

Exit ticket · 3 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. The halogens: which statement is true? (Halogens are found as single atoms. / Boiling points of halogens decrease down the group. / Fluorine is the most reactive halogen. / Iodine is more reactive than chlorine.) → Fluorine is the most reactive halogen.Prompt: Which halogen is at the top of the group?
  2. Halogens exist as molecules. What is the formula of a chlorine molecule? (Cl₂ / Cl₃ / Cl⁻ / Cl) → Cl₂Prompt: Halogens are diatomic.

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/ 6

  1. Question 1

    Which halogen is a red-brown liquid at room temperature?

    • A. chlorine
    • B. iodine
    • C. fluorine
    • D. bromine

  2. Question 2

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

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

  3. Question 3

    The halogens: which statement is true?

    • A. Halogens are found as single atoms.
    • B. Iodine is more reactive than chlorine.
    • C. Boiling points of halogens decrease down the group.
    • D. Halogens react with metals to form salts.

  4. Question 4

    Why does reactivity decrease down group 7?

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

  5. Question 5

    Why is chlorine added to drinking water and swimming pools?

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

  6. Question 6

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

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

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Answer key: Group 7: the halogens and displacement

  1. 1. D. bromine

  2. 2. A. yes: chlorine displaces bromine

  3. 3. D. Halogens react with metals to form salts.

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

  5. 5. D. to kill microorganisms

  6. 6. A. yes: chlorine displaces iodine