Covalent Bonding (Oxford AQA IGCSE Combined Science Double Award)

What is Covalent Bonding?

• Non-metal atoms can share electrons with other non-metal atoms to obtain a full outer shell of electrons

• When two atoms share pairs of electrons, they form covalent bonds

• Covalent bonds between atoms are very strong

• When two or more atoms are covalently bonded together, they form ‘molecules’

• Covalently bonded substances may consist of simple molecules or giant molecules (also known as macromolecules)

  • Simple molecules include oxygen and water 

  • Giant covalent structures include diamond and silicon dioxide 

• Weak intermolecular forces exist between individual molecules

  • For example, in methane, each molecule consists of four hydrogen atoms covalently bonded to a carbon atom, and in between individual methane molecules there are weak intermolecular forces

• Shared electrons are called bonding electrons and occur in pairs

• Electrons on the outer shell which are not involved in the covalent bond(s) are called non-bonding electrons

Covalent Bonding Diagram

Simple Covalent Molecules

• Covalent substances tend to have simple molecular structures 

• These small molecules are known as simple molecules

• Small covalent molecules can be represented by dot and cross diagrams

• You need to be able to describe and draw the correct dot-and-cross diagrams, as shown, for the following molecules:

  • Hydrogen (H₂)
    

    

  • Chlorine (Cl₂)
    

    

  • Oxygen (O₂)
    

    

  • Nitrogen (N₂)
    

    

  • Hydrogen chloride (HCl)
    

    

  • Water (H₂O)
    

    

  • Ammonia (NH₃)
    

    

  • Methane (CH₄)

    

Extension Tier Only

• Other simple molecules and giant structures can be given

• This will be shown by a shared pair of electrons or the line(s) for the covalent bond between atoms

Ethene dot-and-cross diagram