Modifications needed to these simple ideas a summary

2 Modifications needed to these simple ideas a summary 

Sizes of ions in solids are found by X-ray crystallography and are termed crystallographic radii . These radii are often used in discussions of properties of electrolyte solutions. But they really should not be used for ions in solution. Many studies indicate that bare ions rarely exist in solution, and their effective size is a combination of the crystallographic radii plus a contribution from solvation effects. Electrochemical experiments can yield solvation numbers, but the main evidence comes from other smdies which will be discussed in Chapter 13. Knowledge about solvation is vital to the understanding of the behaviour of electrolyte solutions and has proved to be of crucial importance in determining the behaviour of biological systems. Because of the considerable current interest in this topic a full chapter will be devoted to solvation. 

Because so much of the theoretical discussions of electrolyte solutions is based on the assumption that ions are spherically symmetrical, there is the tendency to forget that many ions are certainly not symmetrical. A conscious effort should be made to think about the shape of an ion as well as its charge. 

Ions such as Ca , Mg , Cl , SO , PO , are nearly spherically symmetrical, as are many of the complex ions found in inorganic chemistry  

Modem theories of electrolyte solutions using statistical mechanical ideas are now able to take cognisance of the shapes of ions (see Sections 10.17.3 and 10.19). 

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