Covalent Bonding (WJEC GCSE Chemistry: Combined Science)

• Covalent compounds are formed when pairs of electrons are shared between atoms
• Only non-metal elements participate in covalent bonding
• As in ionic bonding, each atom gains a full outer shell of electrons, giving them a noble gas electronic configuration
• Covalently bonded substances may consist of small molecules or giant molecules
• When two or more atoms are covalently bonded together, we describe them as ‘molecules’
• Dot-and-cross diagrams can be used to show the electronic configurations in simple molecules
  • Electrons from one atom are represented by a dot, and the electrons of the other atom are represented by a cross
  • The electron shells of each atom in the molecule overlap and the shared electrons are shown in the area of overlap
  • The dot-and-cross diagram of the molecule shows clearly which atom each electron originated from

Diagram to show the formation of a covalent bond

A covalent bond is the sharing of a pair of electrons between non-metal atoms

Dot and Cross Diagrams for Simple Molecules

• Many simple molecules exist in which two adjacent atoms share one pair of electrons, also known as a single covalent bond (or single bond)

Hydrogen:

Chlorine:

Water:

Methane:

Ammonia:

Hydrogen chloride:

Higher Tier 

Dot and Cross Diagrams for Complex Molecules

• Some atoms need to share more than one pair of electrons to gain a full outer shell of electrons
• If two adjacent atoms share two pairs of electrons, two covalent bonds are formed, also known as a double bond
• If two adjacent atoms share three pairs of electrons, three covalent bonds are formed, also known as a triple bond

Carbon dioxide:

Oxygen:

Nitrogen: