Summary of Lesson on Complex Salts

 In the past two days, we have been looking at the concept of complex salts and I want us to tie it up today so that we can look at other topics also. I will recap the highlights of our discussion to make it easier for you to remember the key points that we have mentioned in the last two days.


I told you that a complex salt contains a complex cation or complex anion or both. The complex cation or anion does have a coordination sphere in which ligands which may be anionic or neutral are bonded to a central metal atom/ion covalently. This is called the coordination sphere of the complex ion. 


The number of ligands found in the coordination sphere is the coordination number of the central atom/ion. The complex ion often have ions that balance the charges and these are called counter ions and are located outside the coordination sphere of the complex ion. The bonding between the complex ion and the counter ions is entirely ionic in nature.


The geometry of the complex ions depend on the number of ligands that are attached to the central metal atom/ion, electronic effects (such as the well known Jahn – Taller effect), steric effects(when bulky ligands are involved) and symmetry of the complex (the point group to which the complex belongs). 


Complex salts often have color for a number of reasons. These reasons would be fully covered when we are discussing coordination chemistry in detail. However, some of these reasons may include;

1) Charge transfer

2) Weak d - d electronic transition

3) A ligand that contains a chromophore. 


Other examples of complex salts include those listed in the image attached to this post. Complex salts are used in dyeing of fabrics, in food preservation, in catalysis and as drugs. 


Tomorrow we shall go further in our discussion about salts by looking generally at the uses of salts. See you then!


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