Diamond and graphite are both made entirely of carbon atoms, yet diamond is extremely hard and ordinarily does not conduct electricity, while graphite is comparatively soft, can slide in layers and conducts electricity. The answer lies in structure and bonding, not in the identity of the element alone. Each carbon in diamond is bonded to four neighbouring carbons in a continuous network; in graphite, each carbon bonds to three neighbours within a sheet, leaving electrons that can move through the layered structure.
This independent eduKateSG Ministry of Education V3.0 Reference 393 focuses on Topic 3.4 Structure and Properties of Materials within the official 2027 Singapore–Cambridge SEC G3 Chemistry K324 syllabus. It compares diamond, graphite and silicon dioxide as giant covalent substances, simple molecular substances such as iodine or methane, poly(ethene), giant ionic lattices and metals or alloys to explain conductivity, hardness, melting behaviour and material use. Twenty-six original worked cases and a twelve-stage diagnostic pathway connect a microscopic structural feature to each visible property.
The syllabus states that candidates need not draw the detailed structures of diamond or graphite. The sketches and examples are conceptual descriptions rather than material-testing instructions or industrial specifications. This deliberately narrower study complements the earlier broad Reference 212 on ionic, covalent and metallic bonding while following the immutable Clementi three-pupil teaching standard. It is independent teaching content, not an official MOE or SEAB examination paper.
1. Locate this topic within K324 without duplicating all bonding
The 2027 K324 Topic 3 includes ionic bonding, covalent bonding, metallic bonding, and structure-and-property relationships. Under 3.4, candidates compare simple molecular substances, macromolecules and giant covalent substances, with silicon dioxide, diamond and graphite named explicitly. They compare diamond and graphite to explain electrical conductivity and lubricating or cutting applications, but detailed structure drawings are not required. The main target is inference: identify the arrangement and mobile particles, then deduce a stated property. This chapter is a focused comparison rather than a second generic overview of all chemical bonds.
2. The same element can have different structures
Diamond and graphite are allotropes of carbon: pure forms of the same element whose atoms are organised differently. Their differing physical properties therefore cannot be explained by saying one contains more oxygen or different protons. Both consist of carbon atoms, and their chemical identity as carbon is the same. What changes is how each carbon is connected to neighbouring atoms and which electrons are available to move. A student who can explain this structural difference can interpret other material examples without assuming that identical chemical composition guarantees identical properties.
3. Diamond’s carbon atoms form a three-dimensional network
In the familiar school model, each carbon atom in diamond is strongly covalently bonded to four other carbon atoms. The bonds form an extended three-dimensional giant covalent lattice, rather than separate small diamond molecules held together by weak intermolecular forces. Breaking or deforming that rigid arrangement requires disrupting strong covalent links in many directions. A pupil should not describe diamond as a packed collection of individual C₄ molecules. The number four describes nearest-neighbour covalent bonding within a continuous network, not a finite molecule formula.
4. Strong covalent bonding explains diamond’s hardness
Diamond has a rigid structure with strong covalent bonds extending through three dimensions. This helps account for its extreme hardness and cutting or abrasive uses under appropriate conditions. Hardness is resistance to scratching or local deformation, not the same property as toughness or resistance to all kinds of impact. Diamond can be brittle and may fracture along particular directions, so ‘diamond is impossible to break’ is inaccurate. A correct school explanation links hardness to the rigid connected network rather than claiming the carbon element is inherently harder in every arrangement.
5. Diamond ordinarily lacks freely mobile electrical carriers
Although diamond contains electrons, its standard pure covalent structure does not provide the mobile charge carriers needed for ordinary electrical conduction in the school model. Strongly bonded electrons are localised within the network, and diamond is therefore described as an electrical nonconductor under standard textbook conditions. This does not imply electrons do not exist in diamond or that specialised modified diamonds have no interesting electronic properties. A pupil should give the syllabus-level reason: lack of mobile delocalised electrons or other suitable carriers, rather than simply say that every covalent substance cannot conduct.
6. Graphite forms bonded sheets rather than a rigid 3D net
In graphite, each carbon atom is covalently bonded to three carbon neighbours within planar layers. These sheets contain strong covalent bonds across their two-dimensional structure, while the interactions between neighbouring layers are much weaker. This arrangement differs from diamond’s four-bond three-dimensional network. A student should not call the bonds within a graphite sheet weak; the important weakness is the attraction between layers. The contrast explains why a block of graphite can be soft or flaky while retaining strong bonding inside each individual sheet.
7. Layers can slide because their interlayer attractions are weaker
Graphite’s sheets can move relative to each other more readily than atoms can rearrange within a diamond lattice. That supports its use as a lubricant or in pencil cores, where small flakes can be transferred to a surface. This does not mean that graphite has low melting point due to weak bonds throughout the whole structure. The strong covalent bonding within layers remains important to its thermal properties. Distinguish the mechanical action of sheet sliding from breaking every carbon–carbon covalent bond in the material.
8. Graphite conducts because some electrons are delocalised
With three sigma-type bonds around each carbon in the simple graphite model, a remaining electron participates in a delocalised system across layers, enabling electrical conduction. The school description is that graphite contains mobile or delocalised electrons that can carry charge. Do not claim graphite conducts because carbon ions move freely in the solid; the carbon lattice remains in place. Directional conduction can vary in real graphite, but the core G3 concept is the presence of mobile electrons in a layered giant covalent structure, unlike ordinary pure diamond.
9. Giant covalent does not mean all substances behave alike
Diamond, graphite and silicon dioxide are giant covalent substances, yet their physical properties are not identical. Both diamond and graphite have extensive strong covalent bonding, but graphite’s layered structure and delocalised electrons alter hardness and conductivity. Silicon dioxide forms a different three-dimensional network involving silicon and oxygen and typically does not conduct electricity as a solid. Students should infer properties from specific connections and mobile particles rather than use the phrase giant covalent as an automatic answer to every question.
10. Silicon dioxide is a connected network, not simple molecules
The formula SiO₂ gives the silicon-to-oxygen ratio in a giant covalent silica network. In the familiar model each silicon is connected through oxygen atoms to other silicon centres, while each bridging oxygen links two silicon atoms. The formula does not require isolated SiO₂ molecules floating between weak attractions in the solid. Strong bonds throughout the network help explain its high melting point and hardness. A pupil who claims silica has a low melting point because it contains only three atoms per formula unit has confused chemical formula ratio with particle structure.
11. Electrical conduction needs the right mobile carriers
For solid metals, delocalised electrons can move through the metallic lattice; for graphite, some electrons are delocalised within its structure; for molten or dissolved ionic compounds, mobile ions can carry charge. These mechanisms differ. Solid sodium chloride has ions but its ionic lattice holds them in fixed positions, so it does not conduct in the usual school test. A student should specify the carriers and whether they can move in the stated physical state. The word conduct alone is incomplete without a mechanism.
12. Solid sodium chloride is not an electronic conductor
An ionic lattice contains positive and negative ions held together by electrostatic attraction. In the solid state those ions are not free to move throughout the lattice, so ordinary solid sodium chloride does not conduct electricity. When molten or dissolved in water, the ions can move and conduct. This differs from graphite, which conducts as a solid through electrons. A pupil who says any material with charged particles conducts must confront the difference between having charges and allowing charge carriers to move. Structure determines mobility, not just the existence of ions.
13. A molten ionic material conducts by mobile ions
When an ionic solid melts, its rigid lattice is disrupted and the ions can move through the liquid. Under an applied potential difference, positive and negative ions migrate in opposite directions and carry electrical charge. A student should not say electrons have become free in the same manner as in a metal, or that the substance now contains entirely new atoms. The ionic identities remain, but their mobility changes with state. An aqueous ionic solution also contains mobile ions, though the exact conductivity depends on concentration and other conditions not specified by a simple diagram.
14. Simple molecular substances have different particles
Methane CH₄ and iodine I₂ are examples of simple molecular substances. Each consists of discrete molecules with strong covalent bonds inside, but intermolecular attractions between separate molecules are generally weaker than the giant network bonds discussed for diamond or silica. As a result, many simple molecular substances have comparatively low melting or boiling points. A pupil who says iodine molecules contain weak covalent bonds because solid iodine can be melted relatively easily has confused intramolecular bonding with intermolecular attractions. State which bonds are broken or overcome during a phase change.
15. Melting a molecular solid need not break covalent bonds
When solid iodine melts, the iodine molecules can move relative to one another after enough intermolecular attractions are overcome. The strong covalent bond within each I₂ molecule is not ordinarily broken merely by that physical melting. This is why the word melting has a different microscopic meaning from a chemical decomposition reaction. Students should identify whether the substance has discrete molecules or a giant network before explaining its thermal behaviour. In graphite or diamond, there are no small individual C molecules whose weak intermolecular forces alone determine the giant solid’s melting behaviour.
16. Poly(ethene) is a macromolecule rather than a simple molecule
Poly(ethene) consists of long covalently bonded chains made from repeated ethene-derived units. Its properties depend on strong bonds along each chain and interactions between chains, which are weaker than the covalent backbone. It is not the same microscopic structure as isolated methane molecules or a diamond network connected in three dimensions. The 2027 Topic 3.4 includes macromolecules as a material category, while the separate organic chemistry topic covers polymer formation in greater detail. A pupil should compare type and scale of structure without duplicating the whole polymerisation syllabus.
17. Metals have positive ions and delocalised electrons
The simplified metallic bonding model represents metal atoms as positive ions in a lattice surrounded by a sea of delocalised electrons. The mobile electrons support electrical and thermal conduction in many metals. Metallic bonding also helps explain why layers of ions can move relative to one another while the electron attraction continues, contributing to malleability. The model is different from an ionic lattice of alternating positive and negative ions. A pupil must not call the mobile carriers in a copper wire free chloride ions or attribute normal metallic conduction to whole atoms moving along the wire.
18. Alloys are mixtures with modified layer movement
An alloy is a mixture of a metal with one or more other elements. If differently sized atoms disrupt the regular arrangement in a pure metal, layers often slide less easily, so the alloy can be harder or less malleable. The syllabus names brass and stainless steel as examples. The useful reasoning is structure to property, not the assumption that every alloy is always harder or lighter under every possible composition and treatment. A student should mention the differing atomic sizes or arrangements and the mechanical obstacle to layer movement rather than merely say adding other elements makes the metal stronger by magic.
19. Hardness and brittleness are different properties
A material can resist scratching but fracture when struck; these are not contradictory descriptions because hardness and toughness describe different responses to applied forces. Diamond is extremely hard yet can be brittle. Graphite is relatively soft in directions associated with layer sliding but still contains strong covalent bonds within its sheets. Students should not use ‘hard’, ‘strong’, ‘tough’ and ‘high-melting’ as interchangeable labels. Each property needs an appropriate microscopic explanation: bond strength, geometry of the network or ability of layers to move.
20. Electrical and thermal conduction are related but not identical
Metals often conduct both electricity and heat well, supported by mobile electrons and other energy-transfer mechanisms. Graphite’s electrical conduction follows delocalised electrons in its layered structure. However a material’s thermal behaviour should not automatically be inferred solely from an electrical test without relevant evidence, because the details of energy transport can differ. The K324 school outcome emphasises explaining named physical properties from structure. State which property is being asked about and name the mobile carriers or bond network actually relevant to it.
21. Compare a solid before and after dissolving
A sample of sodium chloride has an ionic lattice as a solid, so the ions do not move freely across the material. Once dissolved in water, ions are free to move in the solution and carry electrical charge. The process of dissolution is different from melting; one uses a solvent while the other changes state by heating. A student who writes that solid salt conducts because the ions are charged has missed the mobility condition. In a multiple-choice question, it is often the physical state rather than the chemical formula that changes the conductivity answer.
22. Chemical formulas and structure diagrams give different information
C denotes the element carbon; C as diamond or graphite does not specify one single structure unless the allotrope is stated. SiO₂ gives a ratio in a giant network, and NaCl gives a one-to-one ionic formula ratio, not one independent sodium-chloride molecule in the solid lattice. CH₄, by contrast, represents a discrete methane molecule. Understanding what each formula does and does not assert prevents students from inventing weak intermolecular forces for every solid just because the written formula is short. Structure interpretation requires both composition and arrangement.
23. Do not generalise from one covalent example to all others
Methane is a simple covalent molecule and a poor electrical conductor in ordinary conditions, while graphite is a giant covalent form of carbon that conducts through delocalised electrons. Diamond is giant covalent and an ordinary nonconductor. Therefore the phrase ‘covalent substances do not conduct’ has exceptions and needs structural qualification. A better answer asks whether the substance has mobile charged carriers. In an ionic solid, ions are fixed; in a metal and graphite, electrons can be mobile. This same question clarifies conductivity across seemingly unrelated materials.
24. Transfer requires explaining properties from an unknown structure
An unseen diagram might show a connected three-dimensional network with no free electrons, a layered network with electron mobility, or a regular metal lattice interrupted by different-sized atoms. The learner should infer hardness, sliding, electrical conduction or comparative malleability from features, without being told ‘diamond’, ‘graphite’ or ‘alloy’. This reverses the memorised textbook direction: instead of listing properties after seeing a famous material name, the student reads the structure and predicts what it could do. That is the core of K324 Topic 3.4 and the purpose of this focused reference.
25. Twelve-stage Structure–Carrier–Property pathway
Stage 1 — Identify the material’s scale
Decide whether the diagram represents small molecules, a giant network, an ionic lattice, metal or polymer chains.
Stage 2 — Name the constituent particles
Atoms, ions, molecules and delocalised electrons are different entities.
Stage 3 — Inspect the bonding
Covalent bonds within layers or networks, ionic electrostatics and metallic bonding have distinct structures.
Stage 4 — Ask which particles can move
Electrical conduction requires an appropriate mobile charged carrier.
Stage 5 — Distinguish bonds from attractions
Do not confuse strong bonds inside molecules with weaker interactions between molecules.
Stage 6 — Read the structure’s dimensions
Diamond forms a three-dimensional network; graphite consists of strongly bonded sheets.
Stage 7 — Explain hardness or sliding
Connect rigid all-direction bonds or weak interlayer movement to the relevant property.
Stage 8 — Explain thermal behaviour
Identify whether melting overcomes intermolecular attractions or disrupts a giant lattice.
Stage 9 — Check physical state
Ionic solids and melts differ in charge mobility; graphite and metals can conduct as solids.
Stage 10 — Interpret an alloy mixture
Different atomic sizes can disrupt layer movement and change physical properties.
Stage 11 — Avoid blanket rules
Check exceptions like graphite before saying all covalent materials are nonconductors.
Stage 12 — Transfer to an unseen diagram
Infer structure and properties without relying on a memorised name.
26. Fictional three-pupil materials tutorial
Three imagined G3 Chemistry students receive three anonymous structural descriptions. Pupil A identifies a three-dimensional covalent network with four carbon neighbours per atom and explains diamond’s hardness. Pupil B identifies a layered three-neighbour carbon structure and explains why graphite can slide and conduct electricity. Pupil C compares an ionic lattice’s mobile-ion requirement with a metallic lattice’s delocalised electrons. They rotate roles, then independently classify silicon dioxide, a simple molecular substance and an alloy based only on structural evidence. The tutor diagnoses the first mistake—particle scale, bond type, charge mobility or layer movement—and retests with an unfamiliar diagram.
27. Twenty-six original worked examples
Worked Example 1 — Four bonds in diamond
An anonymous solid is described as carbon atoms each covalently bonded to four neighbours in a continuous three-dimensional network. This is diamond in the school model, explaining strong structural rigidity rather than separate carbon molecules.
Worked Example 2 — Three bonds in graphite
A material contains carbon atoms with three strong covalent connections each within flat sheets. The arrangement describes graphite; its layered geometry differs from diamond even though both consist only of carbon.
Worked Example 3 — Diamond’s ordinary electrical behaviour
A diagram of pure diamond shows no freely mobile delocalised electrons as charge carriers. It is ordinarily an electrical nonconductor. The explanation concerns carrier mobility, not the absence of electrons from carbon atoms.
Worked Example 4 — Why graphite conducts
Graphite layers include a system of delocalised electrons available to carry charge. Therefore graphite can conduct as a solid, providing an important exception to the claim that all covalent solids are insulators.
Worked Example 5 — Why graphite slides
Weak interactions between graphite’s strongly bonded carbon sheets allow the layers to move relatively easily. This explains graphite’s lubricating or pencil-marking behaviour, not an absence of strong bonds inside each layer.
Worked Example 6 — A hard cutting material
A named carbon allotrope has a rigid three-dimensional covalent network and great scratch resistance. Diamond is an appropriate syllabus example for cutting or abrasive use because its connected structure resists local deformation.
Worked Example 7 — Hardness does not guarantee toughness
A fictional advertisement says diamond cannot fracture because it is hard. That is wrong: resistance to scratching and resistance to fracture under impact are different properties. A correct answer describes the rigid network without claiming indestructibility.
Worked Example 8 — Silicon dioxide as a giant structure
SiO₂ is represented as a continuous network in which silicon and oxygen atoms are covalently linked. Its formula expresses a ratio in the network, not isolated little SiO₂ molecules held by weak attractions.
Worked Example 9 — Silica’s melting behaviour
A giant covalent silicon dioxide structure requires considerable energy to disrupt the extensive strong bonding for melting. It is not comparable to melting a simple molecular solid merely by overcoming weak forces between small molecules.
Worked Example 10 — Graphite’s high melting character
Graphite layers slide easily yet still contain strong covalent bonds within sheets. Its weak interlayer interactions do not mean every bond in graphite is weak or that it has the same low melting behaviour as a simple molecular substance.
Worked Example 11 — Methane’s molecular structure
CH₄ consists of discrete covalent molecules, unlike a diamond network. Its low boiling behaviour relative to giant covalent solids is associated with the attractions between separate molecules rather than rupture of all C–H bonds.
Worked Example 12 — Iodine as a simple molecular solid
Solid iodine consists of I₂ molecules. The attractions between molecules can be overcome in a physical phase change without breaking the covalent I–I bond in every molecule. Distinguish intermolecular forces from intramolecular bonding.
Worked Example 13 — Iodine melting explanation
A pupil claims iodine melts because its I–I covalent bond is weak. The more appropriate school explanation is that the forces between separate I₂ molecules are overcome; the covalent bond within each molecule remains.
Worked Example 14 — Solid sodium chloride and current
An ionic crystal contains positively charged sodium and negatively charged chloride ions held at fixed lattice sites. Despite charges being present, the solid does not conduct in the ordinary model because its ions cannot move freely.
Worked Example 15 — Molten sodium chloride and current
When ionic sodium chloride melts, its ions become mobile and can carry charge. This differs from metallic conduction, where delocalised electrons are the usual mobile charge carriers in the solid.
Worked Example 16 — Aqueous sodium chloride and current
Dissolving NaCl in water gives mobile Na⁺ and Cl⁻ ions, permitting conduction. The carriers are ions in the solution, not delocalised electrons as in a copper wire.
Worked Example 17 — Metallic electrical conduction
A copper-like metal lattice contains positive ion cores and mobile delocalised electrons in the school bonding model. These electrons provide an electrical conduction mechanism even while the metal remains solid.
Worked Example 18 — Metallic malleability
Regular layers in a pure metal can shift relative to one another while delocalised electrons maintain attractive metallic bonding. This supports malleability and contrasts with brittle fracture of some ionic crystals when their layers are displaced.
Worked Example 19 — Alloy layers and different atom sizes
A fictional alloy contains a mixture of different-sized atoms in a metallic structure. Their disturbed arrangement can hinder easy layer sliding, making it harder than an otherwise comparable pure metal.
Worked Example 20 — Brass as a material mixture
Brass is an alloy of copper and zinc. It is not a new single element and its structure or properties depend on composition. A student should classify it as an alloy mixture rather than a compound with one fixed copper-to-zinc formula.
Worked Example 21 — Poly(ethene) as macromolecules
Poly(ethene) contains long covalently bonded chains and weaker interactions between separate chains. It is a macromolecular material, not a simple two-atom molecule or a three-dimensional diamond network.
Worked Example 22 — The formula I₂ identifies molecules
I₂ denotes a diatomic iodine molecule. This formula helps distinguish a simple molecular iodine solid from giant covalent graphite, whose material name does not denote discrete two-carbon molecules.
Worked Example 23 — The formula C needs structural context
Both diamond and graphite contain carbon and may be written C in chemical descriptions. The formula alone does not determine their electrical conductivity or mechanical properties without the allotrope’s structure.
Worked Example 24 — The formula SiO₂ is a ratio
A silica network has one silicon per two oxygen atoms as a bulk formula ratio. That does not make it a small covalent molecule with only three atoms. Connected structure explains its behaviour.
Worked Example 25 — Compare two carbon structures
Diamond and graphite both contain extensive strong carbon covalent bonds and resist melting readily, yet only graphite provides the usual delocalised-electron conduction and easily sliding layers. State both similarity and difference.
Worked Example 26 — Infer an unseen layered conductor
An unfamiliar material diagram shows bonded sheets with mobile electrons and comparatively weak interlayer attractions. It is consistent with a graphite-like layered giant covalent structure, predicting conduction and easier interlayer sliding without relying on a supplied name.
28. Ten common errors and their precise repairs
1. Claiming all covalent structures are nonconductors
Graphite is a giant covalent exception with delocalised electrons. The correct test is whether appropriate charged carriers can move through the material.
2. Calling the bonds inside graphite layers weak
The carbon covalent bonds within a sheet are strong. Layers slide because interlayer attraction is much weaker, so do not misidentify the location of the weaker interaction.
3. Saying diamond contains individual C₄ molecules
Each carbon forms four bonds in an extended network; there are no separate C₄ units representing the giant diamond structure. Four describes neighbouring atoms.
4. Assuming graphite is soft because it lacks strong bonds
Graphite has strong intralayer covalent bonding but layers can slide. Separate hardness response from melting behaviour and from bond strength in a different direction.
5. Equating hardness and indestructibility
Diamond is hard but can be brittle. Mechanical properties such as hardness and toughness are different, and one should not be used as proof of every other.
6. Explaining solid salt conduction from the presence of ions alone
Ions are charged but fixed in an ordinary solid ionic lattice. Molten or dissolved ions can move and conduct; solid and liquid states matter.
7. Treating graphite’s carriers as mobile carbon ions
Graphite electrical conduction is associated with delocalised electrons, not carbon atoms or ions freely moving through a solid sheet.
8. Calling silicon dioxide separate three-atom molecules
SiO₂ is a ratio in a giant covalent network. Its high melting behaviour comes from extensive strong covalent bonds, not weak attraction among tiny SiO₂ molecules.
9. Assuming all metals and alloys have identical properties
Alloying changes atomic arrangements and can hinder layers sliding. State which structural difference supports the particular claimed mechanical effect.
10. Using composition alone to determine material properties
Diamond and graphite both contain carbon, yet differ profoundly because bonding arrangement and electron mobility differ. Read the structure, not just the element symbol.
29. A ninety-minute three-pupil materials lesson
Begin with three anonymous particle drawings: a four-connected carbon network, three-connected carbon sheets and a metal lattice with mobile electrons. Ask each pupil to identify the structure from evidence rather than the sample name. Next compare conductivity, hardness and melting behaviour, requiring a named carrier or bond arrangement for every conclusion. Introduce solid versus molten sodium chloride and iodine molecules as contrasts, then show a pure metal and an alloy with differently sized atoms. Each pupil rotates roles, and the lesson closes with independent explanation of a new diagram that does not reveal its material. Diagnose the earliest weakness in particle scale, bonding, carrier mobility or interlayer forces.
30. Depth–Load–Transfer diagnostic
Depth means knowing why diamond has four-neighbour bonding while graphite has three-neighbour sheets and mobile electrons, and why strong intralayer covalent bonds coexist with easy interlayer sliding. Load combines structure, solid versus liquid state, charge carriers, hardness, thermal behaviour and the distinction between molecules, ions and lattices. Transfer is demonstrated when the student predicts properties from an unfamiliar network without a material name. The tutor should ask ‘Which particle can move?’ or ‘Which bond would have to be broken?’ rather than simply repeat a paragraph about graphite. That turns memorised facts into scientific inference.
31. Independent practice and checks
Explain why a graphite pencil core leaves marks but a diamond cutting surface behaves differently; identify whether an illustrated SiO₂ structure is a simple molecule or a giant covalent network; compare solid and molten sodium chloride for electrical conductivity; state why an ordinary copper wire conducts in the solid state; and explain why brass can differ mechanically from a pure metal. Finish by classifying three fictional unlabeled materials from descriptions of their connected particles and moving charges. The answer should use a structural explanation rather than rely solely on a property label such as ‘hard’, ‘soft’ or ‘shiny’.
32. Frequently asked questions
How many neighbours does carbon have in diamond?
Each carbon atom is covalently bonded to four other carbon atoms in a giant three-dimensional network.
How many neighbours does carbon have in graphite?
Each carbon is bonded to three neighbours within a sheet in the school model.
Why is diamond hard?
Its rigid three-dimensional giant covalent network resists local deformation.
Why can graphite lubricate?
Its strongly bonded sheets can slide relative to one another due to weaker interactions between layers.
Why does graphite conduct electricity?
It has mobile delocalised electrons in its layered bonding structure.
Does diamond usually conduct electricity?
Pure diamond is ordinarily an electrical nonconductor in the standard school model.
Why does silicon dioxide have a high melting point?
Its extensive giant covalent network requires considerable energy to disrupt.
What carries current in molten ionic compounds?
Mobile positive and negative ions, rather than ordinary metallic delocalised electrons.
Why do metals usually conduct as solids?
They have delocalised electrons that can move through the metallic structure.
What distinguishes an alloy from a pure metal?
It mixes a metal with other element(s), often modifying regular layer arrangements and material properties.
33. Closing principle
Composition alone does not determine a material’s behaviour. Diamond and graphite contain the same carbon element, but their covalent networks and available mobile electrons differ. A correct learner can account for diamond’s hardness, graphite’s sliding and conduction, silica’s giant network, ionic state-dependent conductivity and metallic properties from microscopic structures. The best test is whether that explanation transfers to an unfamiliar structural diagram rather than merely repeating the properties of named substances.
Official syllabus and connected eduKateSG references
Official SEAB 2027 G3 Chemistry K324 Topic 3.4 Structure and Properties · Reference 212 — Ionic, Covalent and Metallic Bonding Overview · Reference 368 — Polymers and Recycling · MOE V3.0 Reference Library · Immutable Clementi three-pupil teaching standard.