Topic 4 - Chemical bonding and structure - 4.3 Covalent structures

Nature of science: Scientists use models as representations of the real world-the development of the model of molecular shape (VSEPR) to explain observable properties. (1.10)


Lewis (electron dot) structures show all the valence electrons in a covalently bonded species.

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 molecule.

Shapes of species are determined by the repulsion of electron pairs according to VSEPR theory.

Carbon and silicon form giant covalent/network covalent structures.

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 nonbonding pairs of electrons.

Prediction of molecular polarity from bond polarity and molecular geometry.

Deduction of resonance structures, examples include but are not limited to C6H6, CO32- and O3.

Explanation of the properties of giant covalent compounds in terms of their structures


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 combination.

Allotropes of carbon (diamond, graphite, graphene, C60 buckminsterfullerene) and SiO2 should be covered.

Coordinate covalent bonds should be covered