Graphite and diamond are both pure carbon. One is one of the softest materials known, used in pencils and lubricants. The other is the hardest natural material known, used to cut steel and drill into rock. Same element. Same atomic mass. Same electron configuration. Entirely different structures — and entirely different properties. This lesson ties together everything in Module 1: how we classify matter (IQ1), how structure determines properties at the particle level (IQ2), and how electron configuration drives the periodic trends that explain it all (IQ3). Chemistry's central theme is also its most powerful: structure determines properties.
The Module 1 Framework
Every topic in Module 1 belongs to this chain. This is the most important thing to understand as you head into exams:
| Property | Diamond | Graphite | Structural reason |
|---|---|---|---|
| Hardness | Hardest natural substance | Soft, slippery | Diamond: each C covalently bonded to 4 others in 3D tetrahedral network — must break covalent bonds to deform. Graphite: layers of hexagonal sheets, only weak dispersion forces between layers → layers slide past each other easily. |
| Electrical conductivity | Insulator | Good conductor (in layer direction) | Diamond: all 4 valence electrons bonded → no delocalised electrons. Graphite: each C uses 3 bonds in plane, leaving 1 electron per C delocalised across the entire layer → mobile π-electron system → conducts electricity. |
| Melting point | >3500°C (sublimes) | ~3600°C (also very high) | Both require breaking C–C covalent bonds to melt (very strong). Despite different structures, both have extremely high MP because covalent network bonding must be overcome. |
| Thermal conductivity | Exceptionally high | Anisotropic (high in plane, low between layers) | Diamond: rigid 3D covalent network conducts heat through phonons efficiently in all directions. Graphite: efficient in-plane but poor between layers (only weak IMFs). |
| Appearance | Transparent, clear | Black, opaque | Diamond: large HOMO-LUMO gap (no visible light absorption). Graphite: delocalised electrons absorb all visible wavelengths → black. |
| Density | 3.51 g/cm³ | 2.09–2.23 g/cm³ | Diamond: denser 3D packing of C atoms. Graphite: layered structure with spacing between layers → less dense. |
Matter → pure substances (elements/compounds) or mixtures (homogeneous/heterogeneous). Separation techniques match to properties: filtration (particle size), distillation (BP difference), crystallisation (solubility/temperature), chromatography (differential distribution), gravimetric analysis (mass of precipitate). Technique choice depends on the physical property difference being exploited.
Bonding type determines all properties. Ionic: strong electrostatic forces, high MP/BP, conducts when molten/dissolved, brittle. Covalent molecular: weak IMFs (dispersion, dipole-dipole, H-bonds), low MP/BP, poor conductor, solubility depends on polarity. Covalent network: covalent bonds throughout, very high MP, insoluble, hard. Metallic: delocalised electrons, conductive, malleable/ductile, variable MP. IMF hierarchy: H-bond > dipole-dipole > dispersion. Polymers: addition vs condensation; thermoplastic vs thermosetting. Solubility: like dissolves like — polarity compatibility determines dissolution.
Atomic models: Dalton → Thomson → Rutherford (gold foil) → Bohr (emission spectra) → quantum mechanical. Subatomic particles: proton, neutron, electron. Isotopes: same Z, different A, same chemistry. Ar = Σ(mass × fraction). Electron configuration: Aufbau, Pauli, Hund's. Subshells: 1s 2s 2p 3s 3p 4s 3d 4p. Periodic trends: across period → ↑Z_eff → ↓radius, ↑IE, ↑EN. Down group → ↑shells → ↑radius, ↓IE, ↓EN. Valence electrons determine ion charge, bond type, and reactivity.
Worked Examples
The most common Module 1 question types and how to approach them:
| Question type | Key approach | Critical phrases to include |
|---|---|---|
| "Explain the high/low MP/BP of X" | Identify bond/IMF type → state its relative strength → link to energy needed to overcome it | "Strong/weak [bond type]... requires large/small energy to overcome... therefore high/low MP" |
| "Compare the conductivity of A and B" | Identify whether each has mobile charge carriers (delocalised electrons or free ions) | "[Substance] has/has no delocalised electrons/free ions... therefore conducts/does not conduct" |
| "Why does [element X] have a lower IE than [element Y]?" | Compare atomic radius and Z_eff → link to ease of electron removal | "X has a larger atomic radius / lower Z_eff... valence electron is further from nucleus / less attracted... lower energy required" |
| "Predict and explain the trend in [property] across Period 3 / down Group 2" | State the direction of change → explain Z_eff/shielding/radius → link to the property | Across period: "Z_eff increases, shielding constant..." Down group: "New shell added, radius increases, more shielded..." |
| "Identify the type of polymerisation and justify" | Check for C=C (addition) or ester/amide links + byproduct (condensation) | Addition: "C=C opens, no byproduct." Condensation: "ester/amide linkage formed, H₂O released" |
Extended Synthesis Activity
1 Silicon (Si) and sodium chloride (NaCl) are both solid crystalline materials at room temperature. However, they have very different properties. Complete the following comparison using your full Module 1 knowledge:
| Property | Silicon | Sodium chloride |
|---|---|---|
| Substance type (element/compound) | ||
| Bonding type | ||
| Structure type | ||
| Melting point (high/low — justify) | ||
| Electrical conductivity (solid/liquid — justify) | ||
| Solubility in water |
2 You are a materials scientist designing a cooking utensil. You need a material that: (a) conducts heat well, (b) does not conduct electricity, (c) has a high melting point, (d) is hard and scratch-resistant. Using Module 1 knowledge, evaluate silicon dioxide (SiO₂ — used in glass and ceramics) against copper (Cu — used in cookware) for each requirement. Which material better satisfies all four requirements? Justify.
3 Extended response: Describe how the electron configuration of carbon explains both its ability to form the covalent network structures (diamond and graphite) and why it does not form simple ionic compounds. In your answer, use evidence from IQ3 (electron configuration) and IQ2 (bonding). 6 MARKS
Multiple Choice
1. (Synthesis) An unknown substance has: high melting point (~2800°C), does not conduct electricity in any state, insoluble in water and organic solvents, extremely hard. The substance is most likely:
2. (Synthesis) The trend in electronegativity across a period and the trend in first ionisation energy across a period both:
3. (IQ1+IQ2 synthesis) A chemist has a mixture of iodine (I₂) and potassium chloride (KCl) dissolved in water. Which method would effectively separate them?
4. (IQ2+IQ3 synthesis) Hydrogen fluoride (HF) has a much higher boiling point (19.5°C) than hydrogen chloride (HCl, –85°C), despite HF having lower molar mass. The correct explanation is:
5. (Full module synthesis — HOT) Graphene is a single layer of graphite. It is the thinnest material known (one atom thick), the strongest material ever measured, an exceptional electrical conductor, and transparent. Which combination of structural features explains ALL four properties?
Short Answer
6. Buckminsterfullerene (C₆₀, "buckyballs") consists of carbon atoms arranged in a hollow spherical cage of 60 carbon atoms (hexagons and pentagons, like a soccer ball). Each C is bonded to 3 others. (a) Classify C₆₀ as ionic, covalent molecular, covalent network, or metallic. Justify. (b) Compare the likely melting point of C₆₀ to diamond and graphite. (c) Would C₆₀ be expected to dissolve in water or in a non-polar solvent like toluene? Justify using IQ2 principles. 5 MARKS
7. Extended response: A student claims: "The periodic table is just a list of elements arranged in alphabetical order of their names." Using evidence and reasoning from IQ3, evaluate this claim. In your answer: (a) identify the actual organising principle, (b) explain why this principle works to group elements with similar chemical behaviour together, and (c) give two specific examples from the periodic table that demonstrate the table's predictive power. 6 MARKS
1. Si: element, covalent network solid (each Si bonded to 4 others tetrahedrally throughout 3D lattice), very high MP (~1414°C) because must break strong Si–Si covalent bonds, poor electrical conductor (semiconductor; valence band full, small band gap), insoluble in water. NaCl: ionic compound, ionic lattice (alternating Na⁺ and Cl⁻ in face-centred cubic array), high but not extreme MP (~801°C) because strong electrostatic forces but weaker than covalent bonds, solid insulates (fixed ions), liquid/aqueous conducts (free ions), soluble in water (ion-dipole forces).
2. SiO₂ ceramic: (a) thermal conductivity — moderate (phonon conduction through rigid covalent network, lower than Cu); (b) electrical insulator ✓ (no free electrons); (c) very high MP ✓ (~1710°C); (d) very hard ✓ (3D covalent network). Cu: (a) excellent thermal conductor ✓ (delocalised electrons); (b) excellent electrical conductor ✗ (fails requirement b); (c) MP 1085°C ✓; (d) moderately hard. Best material for all 4 requirements: SiO₂ ceramic satisfies b, c, d better, though with lower thermal conductivity than Cu. Copper fails requirement (b). A ceramic (SiO₂-based) would be the better choice if all four properties are equally required.
3. C (Z=6): config [He]2s²2p² with 4 valence electrons (Group 14, Period 2). To form C⁴⁺ (ionic): would require removing all 4 valence electrons; cumulative IE₁+IE₂+IE₃+IE₄ is enormous (IE₁=1086, IE₂=2353, IE₃=4621, IE₄=6223 kJ/mol) — total ~14,000 kJ/mol. No chemical reaction releases enough energy to compensate. To form C⁴⁻: gaining 4 electrons would require enormous electron-electron repulsion in a small C atom. Energetically, covalent sharing is overwhelmingly preferred. In diamond: C uses all 4 valence electrons in sp³ hybridised C–C bonds, forming a 3D tetrahedral network — each C bonded to 4 others. The result is an extremely rigid, non-conducting, transparent lattice. In graphite: C uses 3 valence electrons in sp² hybridised C–C bonds within planar hexagonal layers; the remaining 1 electron per C forms a delocalised π system across the entire layer. This explains conductivity and softness (layers slide easily). Same element, same valence electron count (4) — different structural arrangements.
1. D — ~2800°C MP: too high for ionic (mostly 600–1000°C) or molecular (< 300°C), but consistent with covalent network. Does not conduct in any state: rules out metals (conduct) and ionic (conducts when molten). Extremely hard + insoluble: covalent network. Example: SiC (silicon carbide), Al₂O₃ (corundum).
2. B — Both EN and IE₁ generally increase left to right due to increasing Z_eff with constant shielding. Both show anomalies (IE: dips at Group 13 and 16; EN is smoother). Both decrease going down a group.
3. C — Solvent extraction: I₂ non-polar → dissolves in hexane (like dissolves like). KCl ionic → remains in water (ion-dipole forces). After shaking with hexane, I₂ partitions into hexane layer; KCl stays in water. Separate layers (hexane floats on water). Filtration won't work (both dissolved). Distillation requires large BP differences and doesn't separate solutes well. Crystallisation doesn't separate I₂ from KCl by crystal shape.
4. A — H-bonding in HF (F is highly electronegative, N–H or O–H or F–H can H-bond). HCl: Cl not electronegative enough for H-bonding → only dipole-dipole (plus dispersion). H-bonds are stronger → higher energy to overcome → higher BP for HF despite lower molar mass.
5. C — Graphene: sp² C–C bonds in hexagonal lattice → strongest bonds → exceptional strength. 3 bonds per C leave 1 electron per C delocalised as π electrons across the layer → conductor. Single atom thick → thinnest possible material → absorbs ~2.3% of visible light (quantum mechanical opacity) → nearly transparent. All properties follow directly from the sp² covalent 2D structure with delocalised electrons.
Q6 (5 marks): (a) C₆₀ is a covalent molecular substance (1 mark). It consists of discrete, closed cage molecules (60 C atoms) — unlike an infinite covalent network lattice (diamond, graphite). Each C is covalently bonded to 3 others within the cage; the C₆₀ molecules are held to each other only by dispersion forces (IMFs between closed-shell molecules). (b) MP of C₆₀ is much lower than both diamond and graphite (~600°C sublimation) (1 mark). Diamond and graphite require breaking C–C covalent bonds throughout their entire structure to melt (>3500°C). C₆₀ only requires overcoming the relatively weak dispersion forces between whole C₆₀ molecules — much less energy (1 mark). (c) C₆₀ is insoluble in water — the non-polar C₆₀ molecule has only dispersion forces, which are incompatible with water's H-bond network; disrupting H-bonds to accommodate C₆₀ provides no compensating interaction energy (1 mark). C₆₀ dissolves in toluene (a non-polar solvent) — dispersion forces between C₆₀ and toluene are compatible; "like dissolves like" — both non-polar (1 mark).
Q7 (6 marks): (a) The student's claim is incorrect. The periodic table is NOT alphabetical — it is organised by increasing atomic number (Z), where Z = number of protons in the nucleus (1 mark). Elements are arranged in 7 periods (horizontal rows) and 18 groups (vertical columns). (b) This principle works because Z determines the electron configuration of an atom. The valence electron configuration (number and type of outermost electrons) determines how atoms bond, what ions they form, and how they react. Elements in the same group have the same number of valence electrons in the same subshell type (e.g. all Group 1 elements have ns¹ valence configuration) → same bonding tendencies → similar chemistry (1 mark). Additionally, the placement by Z resolves anomalies that Mendeleev's mass-based table could not: Te (Z=52) correctly precedes I (Z=53) by Z-ordering, consistent with their chemical group memberships (Group 16 and 17 respectively) (1 mark). (c) Example 1: All Group 1 alkali metals (Li, Na, K, Rb, Cs, Fr) react with water to form M⁺(aq) + OH⁻(aq) + H₂(g). The same reaction type occurs because all have ns¹ valence configuration and a single electron to lose. The vigour increases down the group as atomic radius increases and IE₁ decreases, but the reaction type is the same — a direct consequence of the shared valence configuration (1 mark). Example 2: Mendeleev used the periodic table's pattern to predict the existence and properties of undiscovered elements — eka-aluminium (predicted 1871, discovered as gallium 1875) and eka-silicon (predicted 1871, discovered as germanium 1886). His predictions (atomic mass, density, valence, oxide formula) were confirmed on discovery, demonstrating the table's genuine predictive power based on periodic patterns in electron configuration (1 mark). Overall: the periodic table is a powerful scientific model — not a list but a predictive framework grounded in the physics of electron configuration (1 mark).
Tick when you've finished all activities and checked your answers.