3.4.7—Coordination bond formation

A ligand acts as a Lewis base and donates an electron pair to a Lewis-acid transition-metal cation, forming a coordinate bond.

Show a coordination bond with an arrow from a ligand lone pair to the metal ion. The arrow records the origin of the shared pair; after formation the bond is not a different electrostatic species from other covalent bonds.

Representative question

[Maximum number: 1]

Outline how ammonia acts as a Lewis base when it forms the complex ion

\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]^{2+}(\mathrm{aq}) .

it donates an electron/lone pair «to $\mathrm{Cu}^{2+}$ »

Marking guidance:

Accept diagram showing coordination
bond from lone pair on N to $\mathrm{Cu}^{2+}$ .

Retrieve the route: classify nucleophiles and electrophiles, show heterolysis, write substitution and addition mechanisms, map Lewis coordination, compare SN1/SN2, and restore aromaticity in benzene substitution.

Check electron-pair arrow origin and destination, leaving-group departure, intermediate identity, carbocation stability and the assessed mechanism boundary.

3.4.7—Coordination bond formation

Coordination Bonds

Explaining Coordinate-Bond Formation

Assessment in practice

Electron-Pair Sharing Summary

Question 1