• Quick retrieval from earlier learning (Electron shells and the periodic table). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. How many electrons does an atom of argon (atomic number 18) have in its outer shell? → 8Prompt: Fill the shells 2, 8, 8 in order.
2. Who arranged the elements in an early periodic table and left gaps for undiscovered elements? (Isaac Newton / Dmitri Mendeleev / Marie Curie / Charles Darwin) → Dmitri MendeleevPrompt: He predicted the properties of gallium and germanium before they were found.
3. How many electrons does an atom of potassium (atomic number 19) have in its outer shell? → 1Prompt: Fill the shells 2, 8, 8 in order.

• Show the periodic table and ask what patterns students can see before anything is explained.
• Share the objective: Predict ion charges from the periodic table. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: Phosphorus (P) is in group 15 (5). What charge does its ion have?
• Step 1: It gains 3 electrons, so the ion is negative.
• Step 2: So the answer is: 3−
• Answer: 3−
• 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. Potassium (K) is in group 1. What charge does its ion have? (3− / 3+ / 2− / 1+) → 1+Prompt: Metals lose their outer electrons; non-metals gain electrons to fill their outer shell.
2. An atom of lithium (atomic number 3) forms its usual ion (charge 1+). How many electrons does the ion have? → 2Prompt: A neutral atom has as many electrons as protons.

• 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.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. An atom of chlorine (atomic number 17) forms its usual ion (charge 1−). How many electrons does the ion have? → 18Prompt: A neutral atom has as many electrons as protons.
2. Why does magnesium oxide have a much higher melting point than sodium chloride? (Magnesium oxide is covalent / Oxygen is a gas / Mg²⁺ and O²⁻ have larger charges, so the ionic bonds are stronger / Sodium chloride has no bonds) → Mg²⁺ and O²⁻ have larger charges, so the ionic bonds are strongerPrompt: Compare the charges on the ions.

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-9.