Infer oxide and chloride bonding from observations
Use melting, conductivity, solubility and water-reaction evidence to suggest bonding types for the specified compounds.
AS Level; Cambridge International Chemistry 9701, 2025–2027 syllabus. Period 3 trends are qualitative unless supplied data are given. Equations show the stated products and conditions; observations and pH depend on concentration and experimental conditions. Written practice is self-checked
Before you begin
- Use electron configurations, oxidation numbers, balanced equations and ionic charges.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Why does a molten ionic compound conduct?
What you will learn
- Distinguish ionic and covalent structures from evidence
- Use conductivity only with phase and mobility stated
- Combine physical and chemical observations
Ionic lattices need mobile ions to conduct
Na₂O, MgO, NaCl and MgCl₂ are modelled predominantly as ionic lattices. They generally have high melting points because of strong electrostatic attractions between oppositely charged ions. A solid ionic lattice does not conduct by ion movement; molten or aqueous ionic material can conduct if ions are mobile.
Some ionic compounds dissolve in water while others react or have limited solubility. Aqueous conductivity shows mobile ions are present but does not alone prove that every original bond was ionic.
Covalent structures have distinct physical evidence
SiO₂ has a giant covalent network, high melting point and no mobile charge carriers. P₄O₁₀, SO₂, SO₃, SiCl₄ and PCl₅ are covalent substances with molecular or molecular-unit behavior; simple molecular compounds generally have lower melting points and do not conduct as pure substances.
Al₂O₃ is a high-melting oxide with complex bonding that the syllabus identifies by both its amphoteric chemical behavior and physical evidence. AlCl₃ and other compounds may show substantial covalent character. Suggest a bonding type from a consistent set of observations; avoid absolute claims from one test.
Pause and explain
What evidence supports a giant-covalent structure for SiO₂?
Worked example
A chloride has a high melting point, does not conduct as a solid, conducts when molten and dissolves to give mobile ions. Suggest a bonding type.
Show the worked solution
- High melting point is consistent with a strong ionic lattice.
- No solid conductivity is expected when ions are fixed.
- Molten ions can move and carry charge.
Answer The observations are consistent with an ionic lattice: ions are fixed in the solid but mobile in the melt.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A solid does not conduct, but its melt conducts and its melting point is high. Suggest a bonding model and explain both observations.
Give me a hint
Consider fixed ions in a solid lattice and their mobility after melting.
Compare my reasoning
- High melting point suggests strong attractions in a lattice.
- Ions are fixed in the solid, so it does not conduct.
- Molten ions move and carry charge.
The evidence supports an ionic lattice: fixed ions make the solid non-conducting; mobile ions make the melt conduct.
Look for these in your work
- Structure suggested
- Solid behavior explained
- Molten behavior explained
A solid has a very high melting point, does not conduct as a solid or liquid, and does not dissolve in water. Which structure is a reasonable suggestion?
Give me a hint
Look for a strong network without mobile charged particles.
Compare my reasoning
- A high melting point suggests strong bonding through the structure.
- No solid or liquid conductivity suggests no mobile ions or electrons.
- A giant covalent network such as SiO₂ is a reasonable model.
A giant-covalent structure is a reasonable suggestion, provided the evidence and known chemical behavior are consistent.
Look for these in your work
- Network bonding considered
- Charge mobility considered
- Inference scoped
A student calls every chloride ionic because it contains Cl. Use NaCl and SiCl₄ to correct the claim.
Give me a hint
Compare formula/phase behavior and reactions with water.
Compare my reasoning
- NaCl is an ionic lattice of Na⁺ and Cl⁻ ions.
- SiCl₄ is a covalent molecular chloride that hydrolyses in water.
- The element bonded to chlorine and observations distinguish bonding; the suffix ‘chloride’ does not decide it.
NaCl is ionic, whereas SiCl₄ is covalent and reacts with water. A compound name containing ‘chloride’ does not determine bonding type.
Look for these in your work
- Two chloride types distinguished
- Chemical behavior cited
- Naming shortcut rejected
Common mistakes
- Claiming any aqueous conductivity proves an ionic solid
- Saying a solid ionic compound conducts because its ions move freely
- Ignoring chemical reaction with water
- Treating all covalent substances as giant covalent structures
What can you explain now?
Why does a molten ionic compound conduct?
Compare with the explanation
Its ions are mobile
Moving charged ions carry current in the melt.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
Which combination of physical and chemical observations can distinguish ionic, giant-covalent and simple-molecular substances?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.