Cambridge IGCSE Chemistry · Syllabus 0620 · Atoms, Elements and Compounds
Covalent bond
What is Covalent bond?
A covalent bond is formed when a pair of electrons is shared between two atoms. The shared pair counts towards the outer shell of both atoms at once, so both reach a noble-gas electronic configuration in the molecules required at this level, with hydrogen reaching two electrons and the other atoms reaching eight. Covalent bonding occurs between non-metal atoms.
This definition is part of the Atoms, Elements and Compounds chapter in Cambridge IGCSE Chemistry.
Common mistakes with Covalent bond
- 6. “Covalent bonds break when a molecular substance boils.” Supplement 2.5.5 Repair Only the weak forces between molecules are overcome. Steam is still made of \(\mathrm{H_2O}\) molecules, each with its covalent bonds intact. Taught fully in Lesson 2.5B. The weak intermolecular forces wording belongs to Supplement 2.5.5; at Core you describe the low melting point rather than explaining it this way.
- 7. “All covalent substances have low melting points.” Core 2.6.1 Repair Only simple molecular covalent substances do. Diamond and graphite are covalent and have very high melting points, because melting them means breaking strong covalent bonds themselves. Extended candidates: silicon(IV) oxide behaves the same way and for the same reason (Supplement 2.6.3). Taught fully in Lesson 2.6A.