Covalent Bonds (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award)): Revision Note

The formation of covalent bonds

Covalent compounds

• 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

Diagram showing how a covalent bond forms between two chlorine atoms

Single covalent bonds

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

Common Examples of Simple Molecules

Hydrogen:

  Chlorine:

 Water:

Methane:

Ammonia:

Hydrogen chloride: