Contents
Independent final check
Explain without the key
describe / state / deduce
Final check
(a) Carbon is 2,4 and chlorine is 2,8,7. Describe how covalent bonds form in tetrachloromethane, CCl4, and describe its dot-and-cross diagram, outer shells only, with dots for carbon and crosses for chlorine. State the noble gas configuration each atom reaches. (b) Supplement: in methanal, CH2O, the carbon atom (2,4) is bonded to two hydrogen atoms and to the oxygen atom (2,6). Deduce the type of bond between carbon and oxygen, and the number of lone pairs on the oxygen atom and on the carbon atom.
describe: give the features or what happens. state: give a concise answer. deduce: reach a conclusion from the information given.
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Scope and sources
Cambridge IGCSE Chemistry 0620 · 2026–2028 v2 · Original learning materials.
Simple molecules and covalent bonds (2.5 Core 1–3, Supplement 4–5): the covalent bond as a shared pair of electrons that gives noble-gas electronic configurations, dot-and-cross diagrams for H₂, Cl₂, H₂O, CH₄, NH₃ and HCl and, in the Supplement, CH₃OH, C₂H₄, O₂, CO₂ and N₂, and the low melting and boiling points and poor electrical conductivity of simple molecular compounds, explained in the Supplement by weak intermolecular forces and no moving charged particles. Giant covalent structures (2.6), metallic bonding (2.7) and formulae (3.1) have their own modules; the shapes of molecules are not in the syllabus.
Apparatus, amounts and times in the experiment are illustrative. Real practical work follows a teacher-approved safety method.
Official Cambridge syllabus