• 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 very tiny mass (about 1/1840 of a proton)? (proton / neutron / electron) → electronPrompt: Two of the particles are in the nucleus.
2. Atomic structure: which statement is true? (Neutrons have a negative charge. / Protons and electrons have the same mass. / An atom has no overall charge because it has equal numbers of protons and electrons. / The plum pudding model is today's accepted model of the atom.) → An atom has no overall charge because it has equal numbers of protons and electrons.Prompt: Where is each particle, and what is its charge?
3. Which particle has a charge of −1? (proton / neutron / electron) → electronPrompt: Two of the particles are in the nucleus.

• 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.

• 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.

• 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? (The foil had holes / Atoms are spread evenly with positive charge / Electrons are heavy / There is a tiny, dense, positively charged nucleus) → 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? (Scientific models change when new evidence is found. / The nucleus is tiny compared with the whole atom. / The electron was discovered before the nucleus. / Rutherford discovered the neutron.) → Rutherford discovered the neutron.Prompt: Did the plum pudding model have a nucleus?

• 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.

• 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? (In the plum pudding model, electrons orbit a nucleus. / The electron was discovered before the nucleus. / Scientific models change when new evidence is found. / Bohr's model put electrons in shells at fixed distances.) → 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? (The foil had holes / Atoms are spread evenly with positive charge / Electrons are heavy / There is a tiny, dense, positively charged nucleus) → There is a tiny, dense, positively charged nucleusPrompt: Alpha particles are positive. What would repel them strongly?

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