● Lewis (electron dot) structures show all the valence electrons in a covalently bonded species.
● The term ‘electron domain’ should be used in place of ‘negative charge centre’.
● Electron pairs in a Lewis (electron dot) structure can be shown as dots, crosses, a dash, or any
● Coordinate covalent bonds should be covered.
● The ‘octet rule’ refers to the tendency of atoms to gain a valence shell with a total of 8 electrons.
● Some atoms, like Be and B, might form stable compounds with incomplete octets of electrons.
● Resonance structures occur when there is more than one possible position for a double bond in a
● Shapes of species are determined by the repulsion of electron pairs according to VSEPR theory.
● Carbon and silicon form giant covalent/network covalent/macromolecular structures.
Allotropes of carbon (diamond, graphite, graphene, C60 buckminsterfullerene) and SiO2 should be
Applications and skills
● Deduction of Lewis (electron dot) structure of molecules and ions showing all valence electrons for
up to four electron pairs on each atom.
● The use of VSEPR theory to predict the electron domain geometry and the molecular geometry for
species with two, three, and four electron domains.
● Prediction of bond angles from molecular geometry and presence of non-bonding pairs of
● Prediction of molecular polarity from bond polarity and molecular geometry.
● Deduction of resonance structures, including C6H6, CO3
2–, and O3.
● Explanation of the properties of giant covalent compounds in terms of their structures.
4.3 Covalent Structure
This video is linking the idea of electron domains of the central atom to the shape of the molecule and hybridisation. SL students do not need to worry too much about hybridisation.
Useful links for research:
Allotropes of carbon
Here are more student resources on wakelet