Once students understand outer-shell electrons and stability, valency stops looking like a random number rule. This lesson turns the stability idea into the logic of electron gain and loss, and introduces cations and anions as the next step toward bonding.
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Many students hear about ions as if atoms change charge for no reason. Before the formal language, write why you think electron gain or loss might happen.
Think about what happens when sodium and potassium atoms interact with water, and why they form charged particles.
Valency makes more sense when students see it as a stability idea, not as a number to memorise without reason.
In this unit, valency is used to describe the combining behaviour of atoms in relation to their outer-shell electrons. Atoms with outer shells that are not yet stable may lose electrons, gain electrons or later share electrons. Valency is the language students use to describe that tendency at the Stage 5 level.
That means valency is not just a label to copy from a chart. It is a way of describing what an atom is likely to do when its outer shell is not yet in a stable arrangement. Once students see that link, the idea becomes more logical and easier to remember.
Atoms do not change the number of protons when they form simple ions in this Stage 5 model. Instead, they gain or lose electrons. If an atom loses electrons, it is left with more protons than electrons and becomes positively charged. If it gains electrons, it ends up with more electrons than protons and becomes negatively charged.
Equal numbers of protons and electrons in the simple model.
Losing one electron leaves the particle positively charged.
Gaining one electron makes the particle negatively charged.
Students do not need every possible ion in this lesson. They need the core logic: electron gain and loss change charge, and that process links back to the idea of a more stable outer shell.
For example, sodium tends to lose one electron because that leaves it with a more stable arrangement. Chlorine tends to gain one electron because that also moves it toward a more stable outer shell. The charges are not random; they are the result of electron change.
Ion formation makes the idea of stability visible. When students understand that losing electrons creates cations and gaining electrons creates anions, they can explain charge changes logically instead of memorising them as isolated facts.
This is also why charge language matters. Positive and negative signs are not decorations added to symbols. They show the balance between protons and electrons after electrons have been lost or gained.
Valency describes the combining behaviour of atoms as they move toward a more stable outer-shell arrangement.
A cation is a positively charged ion formed when an atom loses electrons.
An anion is a negatively charged ion formed when an atom gains electrons.
Ion formation links outer-shell stability to the charged particles students describe in chemistry.
Explain why losing electrons creates a positive ion and gaining electrons creates a negative ion.
Write a short explanation showing how valency, ion formation and stability are connected.
Claim: State your position or answer clearly.
Evidence: Use facts and concepts from the lesson.
Reasoning: Explain how the evidence supports your claim.
1. What is valency used to describe at Stage 5?
Which option does not describe what valency is used for at Stage 5?
2. How is a cation formed?
3. Why is an anion negatively charged?
4. Which statement best links ion formation to the stability idea from Lesson 06?
5. Which statement best explains why sodium forms a positive ion?
Explain what a cation is and what a positive charge means in terms of protons and electrons. 1 mark for defining a cation. 1 mark for explaining it forms by losing electrons. 1 mark for explaining positive charge means more protons than electrons.
Explain why an atom might gain electrons to form an anion. 1 mark for explaining that gaining electrons moves toward stability. 1 mark for explaining that more electrons than protons creates negative charge. 1 mark for defining anion. 1 mark for linking back to the stability idea.
Why is valency easier to understand after learning about outer-shell electrons and stability? 1 mark for explaining that valency connects to outer-shell electrons. 1 mark for explaining that stability gives a reason for the number. 1 mark for explaining that without stability it seems random. 1 mark for linking to ion formation logic.
Return to the opening question. Can you now explain why atoms may gain or lose electrons using stability and charge language?
1: A. Valency describes the combining behaviour of atoms as they move toward stability.
2: C. A cation is formed by losing electrons.
3: B. An anion is negative because it has gained electrons and now has more electrons than protons.
4: D. Ion formation is linked to the move toward a more stable outer shell.
5: B. Sodium becomes positive when it loses an electron and is left with more protons than electrons.
Sample answer: A cation is a positively charged ion. It forms when an atom loses electrons. Positive charge means the particle has more protons than electrons.
1 mark for defining a cation. 1 mark for explaining it forms by losing electrons. 1 mark for explaining positive charge means more protons than electrons.
Sample answer: An atom may gain electrons because this can move it toward a more stable outer-shell arrangement. This forms an anion because gaining electrons gives the particle more electrons than protons, so the charge becomes negative. This links to stability because the change is part of reaching a more favourable arrangement.
1 mark for explaining that gaining electrons moves toward stability. 1 mark for explaining that more electrons than protons creates negative charge. 1 mark for defining anion. 1 mark for linking back to the stability idea.
Sample answer: Valency is easier to understand because students already know that outer-shell electrons and stability matter in chemical behaviour. Without the stability idea it would seem like a random number rule. This matters because Stage 5 bonding is more logical when students see the pattern behind it.
1 mark for explaining that valency connects to outer-shell electrons. 1 mark for explaining that stability gives a reason for the number. 1 mark for explaining that without stability it seems random. 1 mark for linking to ion formation logic.
Valency describes combining behaviour in relation to stable outer-shell arrangements.
Cations form when atoms lose electrons and become positively charged.
Anions form when atoms gain electrons and become negatively charged.
Students should now be able to explain how electron gain or loss changes charge and forms ions.
Speed through questions on ion formation, ionic bonding and compound properties. Transfer electrons, transfer the win!