Structure 2.4 Flashcards

(1) Average electronegativity of the bonded atoms (x-axis) and (2) Difference in electronegativity (ΔEN) between them (y-axis). You must show BOTH calculations for full marks.

Top vertex = Ionic (high ΔEN, medium avg EN, e.g. NaCl). Bottom-right = Covalent (low ΔEN, high avg EN, e.g. Cl₂). Bottom-left = Metallic (low ΔEN, low avg EN, e.g. Na).

Bonding is a continuum, not a simple classification. Most bonds exhibit a mixture of character. E.g. AlCl₃ is classified as ionic but behaves as a covalent dimer when vaporised. Always discuss bonding as a continuum.

Na₂O, MgO = giant ionic (high mp, basic). Al₂O₃ = transitional (significant covalent character due to small Al³⁺). SiO₂ = giant covalent (very high mp). P₄O₁₀, SO₃, Cl₂O = simple molecular (low mp, acidic solutions).

Bronze = Cu + Sn (tools, bells). Brass = Cu + Zn (plumbing, musical instruments). Stainless steel = Fe + Cr + Ni + C (surgical instruments, cookware - Cr forms self-healing oxide layer).

An alloy is a MIXTURE of a metal with other metals or non-metals. Using the word “compound” will lose you the definition mark. The components are not chemically bonded in fixed ratios.

A single layer of sp²-bonded carbon atoms (one atom thick). Strongest known material, excellent electrical conductor (delocalised π electrons), transparent, and flexible.

sp³ (diamond): 4 single C-C bonds per carbon, tetrahedral (109.5 deg), no delocalised electrons → electrical insulator, extremely hard 3D giant covalent network. sp² network allotropes (graphite, graphene): 3 σ bonds + 1 delocalised π electron per carbon → electrical conductor along 2D planar sheets. (In contrast, carbon nanotubes are cylindrical rolls and C₆₀ fullerene is a discrete molecular cage with limited conductivity).

C₆₀ = spherical cage molecule (truncated icosahedron), soluble in non-polar solvents, used in drug delivery. CNTs = graphene rolled into cylinders, extraordinary tensile strength and thermal conductivity, used in microelectronics.

Monomers with a C=C double bond undergo polymerisation. The π bond breaks and freed electrons form new C-C σ bonds. No atoms are lost - everything in the monomer appears in the polymer.

Ethene → Polyethene (PE, bags). Chloroethene → PVC (pipes). Tetrafluoroethene → PTFE/Teflon (non-stick). Phenylethene → Polystyrene (PS, insulation).

1) Break the C=C into C-C single bond. 2) Add extension (trailing) bonds at each end. 3) Enclose in square brackets with subscript n. Full marks require BOTH trailing bonds outside brackets AND subscript n.

The polymer backbone consists of strong, saturated C-C single bonds that are chemically inert. There are no functional groups for enzymes or water to attack, so they persist in the environment.

Monomers with TWO functional groups (bifunctional) react, releasing a small molecule (usually H₂O) at each linkage. Unlike addition, atoms ARE lost.

Polyester: diol (-OH) + dicarboxylic acid (-COOH) → ester linkage (-COO-), e.g. PET. Polyamide: diamine (-NH₂) + dicarboxylic acid (-COOH) → amide linkage (-CONH-), e.g. Nylon-6,6. Both lose H₂O.

Addition: unsaturated C=C monomers, no small molecules eliminated (100% atom economy), non-biodegradable hydrocarbon backbone. Condensation: monomers with two reactive functional groups, small molecule (e.g. H₂O, HCl) eliminated per linkage, hydrolysable backbone → potentially biodegradable.

Each monomer needs a functional group at BOTH ends to react and continue the chain. If a monomer only has one functional group, the chain terminates immediately - no polymer can form.

Usually H₂O, but can also be HCl (e.g. When acyl chlorides are used as monomers). Always identify the specific small molecule in your answer - don’t assume water.