Dative Covalent Bonding (AQA AS Chemistry): Revision Note

Dative Covalent Bonding

• In a simple covalent bond, the two atoms involved share a pair of electrons

• Some molecules contain a lone pair of electrons that can be donated to form a bond with an electron-deficient atom

• An electron-deficient atom has an unfilled outer orbital and can accept a pair of electrons

• In this type of bond, both electrons come from the same atom

  • This is called dative covalent bonding, also known as coordinate bonding

• An example of a dative covalent bond occurs in the ammonium ion

• The hydrogen ion, H⁺, is electron-deficient and has space for two electrons in its outer shell

• The nitrogen atom in ammonia has a lone pair of electrons, which it donates to the hydrogen ion to form the dative covalent bond

• Aluminium chloride also involves dative covalent bonding

• At high temperatures, aluminium chloride exists as a monomer, AlCl₃.

• This molecule is electron-deficient because the aluminium atom does not have a full outer shell and needs two more electrons

• At lower temperatures, two AlCl₃ molecules join together to form a dimer, Al₂Cl₆.

• This occurs because lone pairs of electrons on two of the chlorine atoms are donated to the aluminium atoms, forming two coordinate bonds between the molecules