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Science lesson plan · 8th grade (Year 9 in England) · 30 minutes

How the model of the atom changed over time

Atoms, elements and the periodic table

CCSS NGSS.HS-PS1-8CCSS NGSS.SEP 7England: GCSE Combined Science: Atomic structure (development of the model of the atom)

Objective and success criteria

Students will: How the model of the atom changed over time.

  • 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: Protons, neutrons and electrons

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 (Protons, neutrons and electrons). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. Which particle has a charge of −1? (proton / neutron / electron) → electronPrompt: Two of the particles are in the nucleus.
  2. Atomic structure: which statement is true? (Most of the mass of an atom is in the nucleus. / Protons and electrons have the same mass. / The plum pudding model is today's accepted model of the atom. / Electrons are found in the nucleus.) → Most of the mass of an atom is in the nucleus.Prompt: Where is each particle, and what is its charge?
  3. Which particle has a charge of +1? (proton / neutron / electron) → protonPrompt: Two of the particles are in the nucleus.

Hook · 3 min

  • Show the periodic table and ask what patterns students can see before anything is explained.
  • Share the objective: How the model of the atom changed over time. 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: Which particle did James Chadwick discover in 1932?
  • Step 1: Chadwick showed the nucleus contains uncharged neutrons as well as protons.
  • Step 2: So the answer is: the neutron
  • Answer: the neutron
  • 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. Which particle did James Chadwick discover in 1932? (the proton / the electron / the photon / the neutron) → the neutronPrompt: It has no charge, which made it hard to detect.
  2. Models of the atom: which statement is NOT true? (Most of the mass of an atom is in its electrons. / The nucleus is tiny compared with the whole atom. / Bohr's model put electrons in shells at fixed distances. / The electron was discovered before the nucleus.) → Most of the mass of an atom is in its electrons.Prompt: Did the plum pudding model have a nucleus?

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 5 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. Models of the atom: which statement is NOT true? (Bohr's model put electrons in shells at fixed distances. / In the plum pudding model, electrons orbit a nucleus. / The electron was discovered before the nucleus. / The nucleus is tiny compared with the whole atom.) → In the plum pudding model, electrons orbit a nucleus.Prompt: Did the plum pudding model have a nucleus?
  2. A very few alpha particles bounced back from the gold foil. What did this show? (Electrons are heavy / The foil had holes / There is a tiny, dense, positively charged nucleus / Atoms are spread evenly with positive charge) → There is a tiny, dense, positively charged nucleusPrompt: Alpha particles are positive. What would repel them strongly?

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: Protons, neutrons and electrons.
  • 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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How the model of the atom changed over time

Name

Date

Score/ 5

  1. Question 1

    A very few alpha particles bounced back from the gold foil. What did this show?

    • A. Atoms are spread evenly with positive charge
    • B. The foil had holes
    • C. Electrons are heavy
    • D. There is a tiny, dense, positively charged nucleus

  2. Question 2

    Models of the atom: which statement is NOT true?

    • A. Scientific models change when new evidence is found.
    • B. Bohr's model put electrons in shells at fixed distances.
    • C. Most of the mass of an atom is in its electrons.
    • D. The electron was discovered before the nucleus.

  3. Question 3

    Which particle did James Chadwick discover in 1932?

    • A. the electron
    • B. the photon
    • C. the neutron
    • D. the proton

  4. Question 4

    Why did scientists replace the plum pudding model?

    • A. Thomson asked them to
    • B. New experimental evidence did not fit it
    • C. It was too complicated
    • D. Plums were unpopular

  5. Question 5

    In Rutherford's experiment, most alpha particles went straight through thin gold foil. What did this show?

    • A. Alpha particles are negative
    • B. Gold has no electrons
    • C. Most of the atom is empty space
    • D. Atoms are solid spheres

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Answer key: How the model of the atom changed over time

  1. 1. D. There is a tiny, dense, positively charged nucleus

  2. 2. C. Most of the mass of an atom is in its electrons.

  3. 3. C. the neutron

  4. 4. B. New experimental evidence did not fit it

  5. 5. C. Most of the atom is empty space