AQA A Level Chemistry

Revision Notes

1.4.3 Covalent Bonding

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

Chemical Bonding Defining Covalent Bonds, downloadable AS & A Level Chemistry revision notes

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

Chemical Bonding Table_8, downloadable AS & A Level Chemistry revision notes

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

Chemical Bonding Single Covalent Bonding Hydrogen, downloadable AS & A Level Chemistry revision notes

Covalent bonding in hydrogen

Chlorine, Cl2

Chemical Bonding Single Covalent Bonding Chlorine, downloadable AS & A Level Chemistry revision notes

Covalent bonding in chlorine

Hydrogen Chloride, HCl

Chemical Bonding Single Covalent Bonding HCl, downloadable AS & A Level Chemistry revision notes

Covalent bonding in hydrogen chloride

Ammonia, NH3

Chemical Bonding Single Covalent Bonding Ammonia, downloadable AS & A Level Chemistry revision notes

Covalent bonding in ammonia

Methane, CH4

Chemical Bonding Single Covalent Bonding Methane, downloadable AS & A Level Chemistry revision notes

Covalent bonding in methane

Ethane, C2H6

Chemical Bonding Single Covalent Bonding Ethane, downloadable AS & A Level Chemistry revision notes

Covalent bonding in ethane

Double covalent bonding

Oxygen, O2

Chemical Bonding Double Covalent Bonding Oxygen, downloadable AS & A Level Chemistry revision notes

Covalent bonding in oxygen

Carbon dioxide, CO2

Chemical Bonding Double Covalent Bonding CO2, downloadable AS & A Level Chemistry revision notes

Covalent bonding in carbon dioxide

Ethene, C2H4

Chemical Bonding Double Covalent Bonding Ethene, downloadable AS & A Level Chemistry revision notes

Covalent bonding in ethene

Triple covalent bonding

Nitrogen, N2

Chemical Bonding Triple Covalent Bonding, downloadable AS & A Level Chemistry revision notes

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, downloadable AS & A Level Chemistry revision notes

Sulfur dioxide, SO2 – dot and cross diagram

Chemical Bonding Expanding the Octet Rule PCl5, downloadable AS & A Level Chemistry revision notes

Phosphorus pentachloride, PCl5 – dot and cross diagram

Chemical Bonding Expanding the Octet Rule SF6, downloadable AS & A Level Chemistry revision notes

Sulfur hexafluoride, SF6 – dot and cross diagram

Exam Tip

Covalent bonding takes place between nonmetal atoms.

Remember to use the periodic table to decide how many electrons are in the outer shell of a nonmetal atom.

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