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Covalent Bonds (CIE IGCSE Chemistry: 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
Examiner Tip
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).
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:
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