Coordinate Bonds (DP IB Chemistry: SL): Revision Note

Coordination bonds

• The IB term is coordination bond, which is also called a coordinate or dative bond

What is a coordination bond?

• In a regular covalent bond, each atom contributes one electron to the shared pair

• In a coordination bond, both electrons in the bond come from the same atom

• This typically occurs when:

  • One atom has a lone pair of electrons

  • The other atom is electron-deficient, i.e. it has an unfilled outer shell

SL example: the ammonium ion (NH₄⁺)

• The hydrogen ion (H⁺) is electron-deficient and can accept a pair of electrons

• The nitrogen atom in ammonia (NH₃) has a lone pair that it donates to the H⁺ ion

• This forms a coordination bond and creates the ammonium ion (NH₄⁺)

HL example: coordination bonding in metal complex ions

• Coordination bonding also occurs in some metal complex ions formed

  • For example, the aluminium(III) hexaaqua ion ([Al(H₂O)₆]³⁺) complex

  • This complex contains six coordination bonds between water molecules and the Al³⁺ ion

  • In each case, the oxygen atom in H₂O donates a lone pair to the metal ion