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.
TOPIC 5 - Solid Structures
Candidates should be able to:
(a) recall and describe the crystal structures of sodium chloride and caesium chloride, including the crystal coordination numbers and a simple explanation of the differences in terms of the relative sizes of the cations;
(b) recall and describe the structures of diamond and graphite and know that iodine forms a molecular crystal; (c) recall and describe the structure of carbon nanotubes and appreciate the analogy with the graphite structure;
(d) understand and explain the simple 'electron sea' model for bonding in metals and use it to explain their physical properties;
(e) explain the relationship between physical properties (e.g. hardness, volatility and electrical conductance) and structure and bonding for the examples above;
(f) understand that a so-called ¡®smart¡¯ material is able to exhibit a change in properties with a change in conditions (temperature, pH, etc) and this is often caused by a change in structure;
(g) understand that nano-sized materials often exhibit different properties which can lead to new uses.
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