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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 is in the nucleus and its number defines the element? (proton / neutron / electron) → protonPrompt: Two of the particles are in the nucleus.
  2. Atomic structure: which statement is true? (Protons and electrons have the same mass. / Neutrons have a negative charge. / Electrons are found in the nucleus. / Most of the mass of an atom is 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. A very few alpha particles bounced back from the gold foil. What did this show? (Electrons are heavy / Atoms are spread evenly with positive charge / There is a tiny, dense, positively charged nucleus / The foil had holes) → There is a tiny, dense, positively charged nucleusPrompt: Alpha particles are positive. What would repel them strongly?
  2. Models of the atom: which statement is NOT true? (The electron was discovered before the nucleus. / The nucleus is tiny compared with the whole atom. / Bohr's model put electrons in shells at fixed distances. / Rutherford discovered the neutron.) → Rutherford discovered the neutron.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 4 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. Which particle did James Chadwick discover in 1932? (the electron / the proton / the neutron / the photon) → the neutronPrompt: It has no charge, which made it hard to detect.
  2. Models of the atom: which statement is NOT true? (The nucleus is tiny compared with the whole atom. / Scientific models change when new evidence is found. / Most of the mass of an atom is in its electrons. / Bohr's model put electrons in shells at fixed distances.) → Most of the mass of an atom is in its electrons.Prompt: Did the plum pudding model have a nucleus?

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

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Date

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  1. Question 1

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

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

  2. Question 2

    Models of the atom: which statement is NOT true?

    • A. In the plum pudding model, electrons orbit a nucleus.
    • B. Bohr's model put electrons in shells at fixed distances.
    • C. Scientific models change when new evidence is found.
    • D. The electron was discovered before the nucleus.

  3. Question 3

    Why did scientists replace the plum pudding model?

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

  4. Question 4

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

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

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

  1. 1. B. Most of the atom is empty space

  2. 2. A. In the plum pudding model, electrons orbit a nucleus.

  3. 3. A. New experimental evidence did not fit it

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