AS and A2 Chemistry notes and resources (WJEC specification) - UNIT CH2. Properties, Structure and Bonding

The uses to which materials can be put depend on their properties, which in turn depend on the bonding and structure within the material. By understanding the relationship between these factors, chemists are able to design new materials. The types of forces that can exist between particles are studied, along with several types of solid structures, in order to illustrate how these factors influence properties. The building blocks of materials are the elements and the relationship of their properties to their position in the Periodic Table is illustrated by a study of the elements of the s-block and Group 7. An introduction to organic chemistry provides the basis for an understanding of how the properties of carbon compounds can be modified by the introduction of functional groups.

4.3 - Shapes of Molecules

Candidates should be able to:

(a) explain what is meant by the terms lone pairs and bonding pairs of electrons and recall and explain the sequence of repulsions between: two bonding pairs; a bonding pair and a lone pair; two lone pairs;

(b) explain the VSEPR principle in terms of minimising the total repulsions between electrons in the valence shell of a given molecule or ion, giving examples where appropriate;

(c) recall and explain the shapes of the species listed (recall of exact bond angles is required for BF3, CH4, SF6 and NH4+) and apply the VSEPR principle to predict or explain the shapes of other specified simple species involving up to six electron pairs in the valence shell of the central atom.