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A coordinate (dative) bond forms when one atom $\frac{the donor}{Lewis base}$ provides both electrons for the shared pair, while the other $\frac{acceptor}{Lewis acid}$ provides an empty orbital. Once formed, the coordinate bond is identical to a regular covalent bond. Lewis acids: electron-pair acceptors with empty orbitals (BF3, AlCl3, FeCl3, H+, metal cations). Lewis bases: electron-pair donors with lone pairs (NH3, H2O, OH-, CN-, halide ions). Key examples: NH4+ formation (N donates lone pair to H+), BF3.NH3 adduct (N donates to B's empty 2p), Al2Cl6 dimer (Cl bridges via coordinate bonds). In BF3.NH3, boron's hybridisation changes from sp2 to sp3. Back bonding is a special pi-coordinate bond: F's filled 2p overlaps with B's empty 2p in BF3, giving partial double bond character and making BF3 a weaker Lewis acid than BCl3. CO has a coordinate bond component in its triple bond (C donates lone pair to O's empty orbital).