2.2.3—Coordination bonds
- Syllabus
- First assessment 2025
- Objective
- 2.2.3
- Level
- SL
Coordination Bonds
In a coordination bond, both electrons in the shared pair come from the same atom. The bond can be represented by an arrow from the electron-pair donor to the acceptor.
Identify the donor atom or ligand and the acceptor, including coordination bonds in transition-element complexes at HL.
In NH₃→BF₃ the nitrogen lone pair supplies both bonding electrons, so the arrow starts at N and ends at B. The arrow records how the pair originated; after formation it is a shared covalent pair, and in a complex the same donor logic identifies each ligand–metal bond.
Identifying Coordination Bonds
Assessment in practice
Representative question
Question 1
[Maximum number: 1]
State the precise type of bond formation between the cyanide ion and the iron ion.
bond
coordination
Marking guidance:
Accept dative/coordination
covalent.
The Covalent Model Summary
Retrieve the covalent pathway: shared pairs and bond order lead to geometry, polarity and molecular polarity; structure determines network properties, IMF behaviour and chromatography; HL representations extend to resonance, formal charge, sigma/pi bonds and hybridization.
Check the representation first, then count domains, apply geometry, identify polarity or forces, and connect the structure to the requested property or HL bonding description.