Chemical Similarity & Reactivity Patterns
15 Questions · 25 Total Marks · Groups, Ion Charges & Formula Prediction
Quick Reference: Groups & Ion Charges
Exam Instructions
- • Attempt all questions before revealing answers.
- • Use exact mark-scheme language — keywords earn marks.
- • Always reference outer-shell electrons in explanation questions.
- • Check the Examiner Trap on every question you found tricky.
Deduce the charge on an ion formed by an element in Group VI of the Periodic Table.
💡 Hint: Think about how many electrons must be gained to achieve a full outer shell.
Deduce the charge on an ion formed by an element in Group III of the Periodic Table.
💡 Hint: How many electrons does a Group III atom lose to achieve a full outer shell?
Explain why Group II elements form ions with a charge of 2+.
💡 Hint: Reference electron configuration and the drive for stability.
An element in Period 3 forms an ion with a charge of 1−. State the Group that this element belongs to.
💡 Hint: Which group needs to gain exactly 1 electron to fill its outer shell?
The element sulfur is in Group VI, Period 3. State the electronic configuration of the sulfide ion (S²⁻) and explain how it was formed from a sulfur atom.
💡 Hint: Sulfur atom: 2,8,6 — what happens when it gains 2 electrons?
Explain why chlorine (Cl) and bromine (Br) have similar chemical properties.
💡 Hint: Think about their outer electron shells — what do they share?
Sodium (Na) and potassium (K) are both in Group I. Explain why they show similar chemical reactions.
💡 Hint: What is the same about the outer shell of every Group I element?
Elements in the same group of the Periodic Table have similar chemical properties. Explain, in terms of electronic structure, why this is the case. Use Group VII as an example.
💡 Hint: Build your answer in 3 steps: outer electrons → what they do → why this leads to similar reactions.
Magnesium (Mg) is in Group II, Period 3. Calcium (Ca) is in Group II, Period 4. Predict two similarities in the chemical reactions of magnesium and calcium.
💡 Hint: What does being in the same group tell us about how they react?
Explain why noble gases (Group 0) are largely unreactive chemically.
💡 Hint: Think about their outer electron shell — what is special about it?
Sodium forms the compound NaCl with chlorine. Given that rubidium (Rb) is also in Group I, predict the formula of rubidium chloride.
💡 Hint: Both Na and Rb are in Group I — what charge do they form? What charge does Cl form?
Magnesium forms MgO with oxygen. Predict the formula of the compound formed between barium (Ba, Group II) and oxygen.
💡 Hint: Ba is in Group II — same as Mg. What formula pattern does Group II follow with oxygen?
Calcium forms CaCl₂ with chlorine. Predict the formula of the compound formed between strontium (Sr, Group II) and bromine (Br, Group VII).
💡 Hint: Consider the charges of Group II and Group VII ions.
Aluminium (Al, Group III) forms Al₂O₃ with oxygen. (a) Predict the formula of the compound formed between aluminium and sulfur (Group VI). (b) Explain how you determined the ratio.
💡 Hint: Al forms Al³⁺. Sulfur forms S²⁻. Use the 'cross-over' method.
Lithium reacts with nitrogen to form lithium nitride, Li₃N. Sodium (Na) is in the same group as lithium. Nitrogen and phosphorus (P) are in the same group. Predict the formula of sodium phosphide and explain your reasoning.
💡 Hint: Na is Group I (1+ ion). P is Group V — how many electrons does it gain?
🔑 Golden Rules for Chemical Similarity Questions
① Never say "same group" alone — always add "same number of outer-shell electrons."
② Ion charge = Group number sign flipped for non-metals (Group VI → 2−) or same for metals (Group II → 2+).
③ Formula prediction: cross the charges — e.g. Al³⁺ + S²⁻ → Al₂S₃.
④ Noble gases are unreactive because of a full outer shell — not because they "have 8 electrons" (He has 2).
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