AQA A Level Chemistry复习笔记1.4.4 Dative Covalent Bonding

Dative Covalent Bonding

 

  • In simple covalent bonds, the two atoms involved share electrons
  • Some molecules have a lone pair of electrons that can be donated to form a bond with an electron-deficient atom
    • An electron-deficient atom is an atom that has an unfilled outer orbital

     

  • So both electrons are from the same atom
  • This type of bonding is called dative covalent bonding or coordinate bonding
  • An example with a dative bond is in an ammonium ion
    • The hydrogen ion, H+ is electron-deficient and has space for two electrons in its shell
    • The nitrogen atom in ammonia has a lone pair of electrons which it can donate to the hydrogen ion to form a dative covalent bond

     

 1.3-Chemical-Bonding-Dative-Covalent-Bonding-Ammonium-ion

Ammonia (NH3) can donate a lone pair to an electron-deficient proton (H+) to form a charged ammonium ion (NH4+)

 

  • Aluminium chloride is also formed using dative covalent bonding
  • At high temperatures aluminium chloride can exist as a monomer (AlCl3)
    • The molecule is electron-deficient and needs two electrons to complete the aluminium atom’s outer shell

     

  • At lower temperatures the two molecules of AlCl3 join together to form a dimer (Al2Cl6)
    • The molecules combine because lone pairs of electrons on two of the chlorine atoms form two coordinate bonds with the aluminium atoms

     

1.3-Chemical-Bonding-Dative-Covalent-Bonding-Aluminium-chloride

Aluminium chloride is also formed with a dative covalent bond in which two of the chlorine atoms donate their lone pairs to each of the aluminium atoms to form a dimer

Exam Tip

In dative covalent bonding, both electrons in the covalent bond are shared by one atom. A dative covalent bond is drawn using an arrow from the donated pair of electrons to the electron-deficient atom.

 

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