Covalent Bonding (Edexcel International A Level Chemistry)

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Covalent Dot & Cross Diagrams

Covalent compounds

  • The atoms in covalent compounds will share their outer valence electrons to achieve a noble gas configuration

 Chemical Bonding Covalent Dot & Cross 1, downloadable AS & A Level Chemistry revision notesChemical Bonding Covalent Dot & Cross 2 (1), downloadable AS & A Level Chemistry revision notesChemical Bonding Covalent Dot & Cross 2 (2), downloadable AS & A Level Chemistry revision notesChemical Bonding Covalent Dot & Cross 3 (1), downloadable AS & A Level Chemistry revision notes 

Dot-and-cross diagrams of covalent compounds in which the atoms share their valence electrons

Double covalent bonding

Oxygen, O2

Chemical Bonding Double Covalent Bonding Oxygen, downloadable AS & A Level Chemistry revision notes

Covalent bonding in oxygen

Carbon dioxide, CO2

Chemical Bonding Double Covalent Bonding CO2, downloadable AS & A Level Chemistry revision notes

Covalent bonding in carbon dioxide

Ethene, C2H4

Chemical Bonding Double Covalent Bonding Ethene, downloadable AS & A Level Chemistry revision notes

Covalent bonding in ethene

Triple covalent bonding

Nitrogen, N2

Chemical Bonding Triple Covalent Bonding, downloadable AS & A Level Chemistry revision notes

Covalent bonding in nitrogen

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

 Chemical Bonding Dative Covalent Bonding Ammonium ion, downloadable AS & A Level Chemistry revision notes

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

Aluminium chloride

  • 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

Chemical Bonding Dative Covalent Bonding Aluminium chloride, downloadable AS & A Level Chemistry revision notes

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

Examiner Tip

Covalent bonding takes place between nonmetal atoms.

Remember: Use the Periodic Table to decide how many electrons are in the outer shell of a nonmetal atom.

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Philippa

Author: Philippa

Expertise: Chemistry

Philippa has worked as a GCSE and A level chemistry teacher and tutor for over thirteen years. She studied chemistry and sport science at Loughborough University graduating in 2007 having also completed her PGCE in science. Throughout her time as a teacher she was incharge of a boarding house for five years and coached many teams in a variety of sports. When not producing resources with the chemistry team, Philippa enjoys being active outside with her young family and is a very keen gardener.