Dative (Coordinate) Bonds: Both Electrons From One Atom
Most covalent bonds share one electron from each atom. In a dative (coordinate) bond, both shared electrons come from the same atom. Here is how to spot one, draw the arrow and explain it the way the exam wants.
What makes a bond dative
In an ordinary covalent bond each atom gives one electron to the shared pair. In a dative (or coordinate) bond, one atom donates a lone pair into the empty orbital of another, so both shared electrons come from the same atom. Once formed, it is identical to any other covalent bond.
Draw it with a full arrow
Show a dative bond as a full arrow pointing from the donor (the atom with the lone pair) to the acceptor (the atom with the empty orbital). In NH4+, nitrogen's lone pair forms the fourth N-H bond, drawn as N→H.
The must-know examples
NH4+ (NH3 + H+), H3O+, the Al2Cl6 dimer, NH3 to BF3, carbon monoxide (CO), and ligands donating lone pairs to metal ions in complexes.
Practise it yourself
Build dot-and-cross diagrams, including the dative-bonded species, in the interactive ChemBank simulation.
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