Your revision route
What you’ll learn
- Distinguish ionic, covalent and metallic bonding using particles and electrons.
- Use ion charges to obtain simple ionic formulae and interpret bonding diagrams.
- Use the particle model to describe changes of state and apply (s), (l), (g) and (aq) correctly.
- Relate giant ionic, simple molecular, polymeric, metallic and giant covalent structures to their properties.
- Explain conductivity by identifying particles that are able to carry charge.
- Compare diamond, graphite, graphene, fullerenes and carbon nanotubes using their structures.
- Explain why alloys can be harder than pure metals.
- For separate Chemistry routes, connect nanoparticle size and surface-area-to-volume ratio to uses and possible risks.
Build the big picture
Key ideas
Bonding begins with electrons
Before naming a bond, identify who has lost, gained or shared electrons—and which particles now attract.
- Ionic bonding follows electron transfer between a metal and non-metal; the bond is the electrostatic attraction between the resulting opposite ions.
- Covalent bonding joins non-metal atoms through shared pairs of electrons.
- Metallic bonding is the attraction between positive metal ions and delocalised electrons throughout a giant structure.
The punchline: Identify the particles first; then name the attraction between them.
Same bond, different architecture
Calling a substance ‘covalent’ is like saying a building uses bricks: the arrangement still decides how it behaves.
- A small molecular substance has strong covalent bonds inside each molecule but much weaker forces between molecules.
- A giant covalent substance has strong bonds extending through a large network.
- Melting point depends on which attractions must be overcome across the whole structure, not on the word ‘covalent’ alone.
The punchline: State the scale and arrangement before explaining a bulk property.
A state symbol is a snapshot
State symbols label a substance's physical form; the particle model tries to explain what is happening underneath.
- Solid particles vibrate in fixed positions; liquid particles stay close but move around one another; gas particles are widely spaced and move freely.
- Melting and freezing occur at the melting point; boiling and condensing occur at the boiling point. Stronger attractions generally need more energy to overcome.
- In equations, (s), (l) and (g) mean solid, liquid and gas; (aq) means dissolved in water.
- Higher Tier: the simple model uses solid, inelastic spheres and omits forces. Real particles are not all solid spheres, and forces do act between them.
The punchline: Use the model as a useful sketch, not a literal portrait of particles.
Bonding is an electron story told three ways
Start with the particles and electrons. The familiar properties follow from what attracts what—and whether any charge carrier can move.
- IonicElectrons transfer; oppositely charged ions attract in a giant lattice.
- CovalentNon-metal atoms share electron pairs within molecules or giant networks.
- MetallicPositive metal ions attract a sea of delocalised electrons.
Charged does not always mean conducting
An ionic lattice contains charged particles, yet the solid refuses to conduct. Movement is the missing ingredient.
- Group 1 and 2 metals commonly form +1 and +2 ions; Group 6 and 7 non-metals commonly form −2 and −1 ions with noble-gas-like outer shells.
- Strong attractions act throughout the giant lattice, so a large energy input is needed to melt it.
- In a solid the ions are fixed. When molten or dissolved, they can move and carry electric current.
The punchline: For conductivity, name the charged particle and say whether it can move.
Melting separates neighbours, not atoms
For a simple molecular substance, melting overcomes forces between molecules—not the covalent bonds inside them.
- Small molecules usually have low melting and boiling points because their intermolecular forces are relatively weak.
- Their covalent bonds remain intact during a change of state.
- Polymer molecules are long chains, with generally stronger attractions between them, so many are solid at room temperature.
The punchline: Always distinguish bonds within molecules from forces between molecules.
Make the model move
Interactive checkpoint
Touch the science. Change a state, build a route or test a relationship.
Join cause to consequence
Match each structure to the property it explains
Choose the most diagnostic property for each structure. Then check the particle-level reason.
Properties are not labels to memorise in isolation; they are consequences of bonding, forces and mobile charge carriers.
Release the charge carriers
When does an ionic substance conduct?
Toggle the physical state. The ions keep their charge; what changes is their freedom to move.
The ions vibrate about fixed lattice positions but cannot travel and carry charge through the crystal.
1 of 3 states explored
Conduction requires charged particles that can move through the material. Fixed ions cannot carry a current from one place to another.
Metals have an electron highway
Delocalised electrons are free to travel through the giant structure, carrying charge and transferring thermal energy.
- Layers in a pure metal can move while metallic attraction is maintained, so the material can bend and be shaped.
- Different-sized atoms in an alloy disrupt the regular layers.
- Those distorted layers find it harder to slide, which can make the alloy harder than the pure metal.
The punchline: Use electron movement for conduction and layer movement for shaping.
Carbon is a master of rearrangement
The same element can become diamond, graphite or graphene. Architecture changes everything.
- Diamond has four bonds per carbon in a rigid 3D network: it is hard, has a very high melting point and has no mobile electrons.
- Graphite has three bonds per carbon in hexagonal layers, with no covalent bonds between layers and one delocalised electron per carbon; it conducts and its layers can slide.
- One-atom-thick graphene is strong and conducting, making it useful in electronics and composites.
The punchline: Same atoms, different arrangement, different properties.
From structure to property without a logical leap
A high-mark explanation travels through four linked questions rather than teleporting from a material name to a fact.
- StructureIs it simple molecular, giant ionic, metallic or giant covalent?
- ParticlesIdentify atoms, molecules, ions or delocalised electrons.
- Forces and movementAsk what must be overcome and which particles can move.
- PropertyConclude melting point, conductivity, strength or malleability.
Carbon can build cages and tubes
A carbon network need not stay flat: its rings can form hollow cages or tiny cylinders.
- Fullerenes are hollow carbon molecules based on hexagonal rings; some structures also contain rings of five or seven carbon atoms.
- Buckminsterfullerene (C₆₀) is spherical, while carbon nanotubes are cylindrical fullerenes far longer than they are wide.
- Fullerene cages can carry molecules or support catalysts; nanotubes are useful in nanotechnology, electronics and strong, light materials.
The punchline: Hollow shape, exposed surface and aspect ratio turn carbon cages into useful tools.
At the nanoscale, surface takes over
Shrink an object far enough and its surface begins to dominate its behaviour.
- Separate Chemistry: atom radius ≈ 0.1 nm; a small molecule is often ≤ 1 nm; nanoparticles are 1–100 nm and can contain roughly a few hundred atoms.
- Fine particles are about 100–2500 nm and coarse particles about 2500–10,000 nm.
- For a cube, SA:V = 6/L. A 100 nm cube gives 0.06 nm⁻¹; a 10 nm cube gives 0.6 nm⁻¹—ten times larger.
- High surface area can make small masses useful in catalysts, medicine or materials, but benefits and possible risks must be judged from evidence.
The punchline: Smaller size raises surface-area-to-volume ratio; it does not prove benefit or harm.
Words worth knowing
Key definitions
- ionic bond
- The electrostatic attraction between oppositely charged ions.
- covalent bond
- A shared pair of electrons that attracts two atomic nuclei.
- metallic bond
- The attraction between positive metal ions and delocalised electrons in a giant structure.
- delocalised electron
- An electron that is not tied to one atom or bond and can move through a larger structure.
- giant ionic lattice
- A repeating three-dimensional arrangement of positive and negative ions.
- intermolecular force
- An attraction between separate molecules rather than a bond within a molecule.
- polymer
- A very large molecule built from a long chain of repeating units.
- giant covalent structure
- A large network in which many atoms are joined by covalent bonds.
- alloy
- A mixture containing a metal and one or more other elements.
- empirical formula
- The simplest whole-number ratio of atoms or ions in a substance.
- graphene
- A single layer of carbon atoms arranged in a graphite-like hexagonal pattern.
- nanoparticle
- A particle with dimensions on the nanometre scale, commonly treated here as about 1–100 nm.
Follow it step by step
Processes to remember
How to identify the likely bond type
- Check whether the substance contains a metal, non-metals or only metal atoms.
- For a metal with a non-metal, electron transfer usually forms ions; attraction between the resulting ions is ionic bonding.
- Non-metal atoms together usually share electron pairs and form covalent bonds.
- A metallic element or alloy uses the metallic model with delocalised electrons.
Exam tip: After naming the bond, identify the particles and the relevant attraction.
How to construct a simple ionic formula
- Write the charge on each ion, using the group pattern where appropriate: Group 1 is +1, Group 2 is +2, Group 6 is −2 and Group 7 is −1.
- Choose numbers of ions so the total positive and negative charges cancel.
- Write the smallest whole-number ratio as subscripts.
- Check that the finished formula has an overall charge of zero.
Exam tip: A formula gives a ratio; it does not show the lattice's shape.
How to read and criticise bonding models
- In a dot-and-cross diagram, use the two symbols to track which atom supplied each outer electron; shared pairs show covalent bonds, while brackets and charges identify ions.
- Check that each ionic diagram has balanced total charge and each covalent diagram has the intended number of shared pairs.
- Use a ball-and-stick model to identify connections or a repeating pattern, but remember that the sticks are not physical rods and the gaps and particle sizes are not shown realistically.
- A flat diagram may hide the three-dimensional arrangement, while a chemical formula gives particle ratios but no spatial structure.
Exam tip: State what a model shows well and one important feature it leaves out.
How to explain a material property
- Name the type and scale of the structure.
- Identify the particles, bonds or intermolecular forces involved.
- State what must move or be overcome.
- Link the required energy or available charge carriers to the observed property.
Exam tip: Keep covalent bonds within molecules separate from forces between molecules.
See the thinking
Worked example
Worked example: infer structure from properties
A solid substance has a high melting point. It does not conduct electricity while solid, but it does conduct when molten. Identify the most likely type of structure and explain all three observations.
- A high melting point suggests a giant structure with many strong attractions to overcome.
- Conduction only after melting points to charged particles that are fixed in the solid but mobile in the liquid.
- That combination is characteristic of a giant ionic lattice.
- The positive and negative ions are strongly attracted, producing the high melting point.
- The solid's ions cannot move, whereas molten ions can move and carry charge.
Answer: The substance most likely has a giant ionic lattice. Strong attractions between oppositely charged ions give a high melting point; the ions are fixed in the solid but mobile when molten, so only the liquid conducts.
The evidence must be used together. A high melting point alone could also fit a giant covalent or metallic structure, but the change in conductivity on melting distinguishes the ionic model.
Protect the marks
Common mistakes
Watch out: Calling an ionic compound a molecule.
Do this instead: Describe it as a giant repeating lattice of ions.
Watch out: Saying atoms become charged because protons move.
Do this instead: Ions form through loss or gain of electrons; the nucleus is unchanged.
Watch out: Saying covalent bonds are broken when a small molecular substance melts.
Do this instead: Melting overcomes forces between molecules; the bonds inside each molecule remain.
Watch out: Explaining solid ionic non-conduction by saying there are no charges.
Do this instead: Charged ions are present, but they are fixed in the solid lattice and cannot flow.
Watch out: Saying every covalent substance has a low melting point.
Do this instead: Small molecular substances tend to melt easily; giant covalent networks have very high melting points.
Watch out: Saying graphite conducts because its layers slide.
Do this instead: Graphite conducts because it contains delocalised electrons; sliding layers explain softness.
Watch out: Saying alloys are harder because their bonds are simply stronger.
Do this instead: Different-sized atoms disrupt regular layers and make layer movement more difficult.
Watch out: Treating (aq) as another symbol for a liquid.
Do this instead: (l) means the substance is in the liquid state; (aq) means it is dissolved in water.
Try it before you move on
Quick check
Say your answer first, then open the card to check it.
What type of bonding is most likely when sodium reacts with chlorine?
Answer: Ionic bonding
Sodium is a metal and chlorine is a non-metal, so electron transfer produces oppositely charged ions.
Calcium ions are Ca²⁺ and fluoride ions are F⁻. What is the formula of calcium fluoride?
Answer: CaF₂
Two F⁻ ions provide a total charge of −2, balancing one Ca²⁺ ion.
Why do many small molecular substances have low boiling points even though their covalent bonds are strong?
Answer: Boiling overcomes the weaker forces between molecules, not the strong covalent bonds inside them.
Only a relatively small energy input is needed to separate the molecules.
Which feature allows graphite to conduct electricity?
Answer: Delocalised electrons that can move through the structure.
Each carbon contributes an electron that is not confined to one covalent bond.
Why is an alloy often harder than the pure metal from which it is made?
Answer: Different-sized atoms disrupt the regular layers and make sliding more difficult.
The distorted arrangement resists layer movement when a force is applied.
Good questions, clear answers
Frequently asked questions
What is the simplest difference between ionic and covalent bonding?
Ionic bonding involves attraction between ions formed after electron transfer. Covalent bonding joins atoms through shared pairs of electrons.
How can a molecule contain strong bonds but still have a low boiling point?
The strong bonds hold each molecule together. Boiling separates whole molecules by overcoming the much weaker attractions between them.
Why do ionic compounds conduct only when molten or dissolved?
Their ions carry charge. In a solid lattice the ions cannot move, but in a liquid or solution they are mobile.
Why does graphite conduct electricity but diamond does not?
Graphite has delocalised electrons that can move through its layers. In diamond, all four outer electrons from each carbon are used in bonds, leaving no mobile charge carriers.
Are nanoparticles automatically safer or more dangerous than larger particles?
No. Their high surface-area-to-volume ratio can change how they behave, so each use needs evidence about benefits, exposure and possible risks. Nanoparticle detail in this guide applies to the separate Chemistry route.
What do (s), (l), (g) and (aq) mean in a chemical equation?
They mean solid, liquid, gas and dissolved in water. Aqueous is not the same as liquid: it means the substance is dissolved in water.
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