A level Chemistry · Edexcel 9CH0 · Topic 2B
Covalent and dative bonding
Key points
- A covalent bond is the electrostatic attraction between two nuclei and a shared pair of electrons between them.
- Double and triple bonds contain more shared pairs; bond length decreases and bond enthalpy increases as bond order goes up.
- A σ bond forms from head-on overlap of orbitals; a π bond forms from sideways overlap of p orbitals and is weaker.
- A dative (coordinate) bond has both electrons supplied by one atom, e.g. in NH₄⁺, H₃O⁺ and Al₂Cl₆. Show it with an arrow from donor to acceptor.
- Draw dot-and-cross diagrams showing outer shells only; some atoms have fewer than eight electrons (BF₃) or an expanded octet (SF₆, PCl₅).
- Once formed, a dative bond is identical to any other covalent bond.
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A covalent bond forms when two atoms share a pair of electrons. Understanding what holds a shared pair in place, and how double bonds and dative bonds differ, is the basis of all molecular chemistry.
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