Covalent Bonding (AQA AS Chemistry): Revision Note
Covalent Bonding
Covalent bonding occurs between two non-metals
A covalent bond involves the electrostatic attraction between nuclei of two atoms and the bonding electrons of their outer shells
No electrons are transferred but only shared in this type of bonding
The positive nucleus of each atom has an attraction for the bonding electrons shared in the covalent bond
Non-metals are able to share pairs of electrons to form different types of covalent bonds
Sharing electrons in the covalent bond allows each of the 2 atoms to achieve an electron configuration similar to a noble gas
This makes each atom more stable
Covalent Bonds & Shared Electrons Table
type of bond | representation | number of electrons |
|---|---|---|
single | C-C | 2 |
double | C=C | 4 |
triple | C≡C | 6 |
Dot & cross diagrams
Dot and cross diagrams are used to represent covalent bonding
They show just the outer shell of the atoms involved
To differentiate between the two atoms involved, dots for electrons of one atom and crosses for electrons of the other atom are used
Electrons are shown in pairs on dot-and-cross diagrams
Single covalent bonding
Hydrogen, H2
Covalent bonding in hydrogen
Chlorine, Cl2
Covalent bonding in chlorine
Hydrogen Chloride, HCl
Covalent bonding in hydrogen chloride
Ammonia, NH3
Covalent bonding in ammonia
Methane, CH4
Covalent bonding in methane
Ethane, C2H6
Covalent bonding in ethane
Double covalent bonding
Oxygen, O2
Covalent bonding in oxygen
Carbon dioxide, CO2
Covalent bonding in carbon dioxide
Ethene, C2H4
Covalent bonding in ethene
Triple covalent bonding
Nitrogen, N2
Covalent bonding in nitrogen
In some instances, the central atom of a covalently bonded molecule can accommodate more or less than 8 electrons in its outer shell
Being able to accommodate more than 8 electrons in the outer shell is known as ‘expanding the octet rule’
Accommodating less than 8 electrons in the outer shell means than the central atom is ‘electron deficient’
Some examples of this occurring can be seen with period 3 elements
Sulfur dioxide, SO2 – dot and cross diagram
Phosphorus pentachloride, PCl5 – dot and cross diagram
Sulfur hexafluoride, SF6 – dot and cross diagram
Examiner Tips and Tricks
Covalent bonding takes place between nonmetal atoms.
Remember: Use the periodic table to decide how many electrons are in the outer shell of a non-metal atom.
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