Covalent Bonding (WJEC GCSE Chemistry)
Revision Note
Covalent Bonding
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:
Examiner Tips and Tricks
When drawing dot-and-cross diagrams for covalent compounds, make sure that the electron shell for each atom is full.
Remember that the 1st shell can only hold 2 electrons.
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