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Werner’s Theory of Coordination Compounds

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Coordination compounds are chemical compounds composed of an array of anions or neutral molecules linked by coordinate covalent bonds to a central atom. Coordination compounds are also known as coordination complexes. The molecules or ions that are connected to the center atom are referred to as ligands (also known as complexing agents).

Metal complexes are coordination compounds in which the central atom is a metallic element. In this type of coordination complex, the central atom is frequently a transition element. It should be noted that the coordination center is the central atom in these complexes.

Properties of Coordination Compounds

  1. Because unpaired electrons absorb light during their electronic transitions, transition element coordination compounds are colored. Iron (II) complexes, for example, can be green or pale green in color, whereas iron(III) coordination compounds are brown or yellowish-brown in color.
  2. When the coordination center is a metal, the resulting coordination complexes have a magnetic property due to the presence of unpaired electrons.
  3. The chemical reactivity of coordination molecules varies. They have the ability to participate in both inner-sphere and outer-sphere electron transfer reactions.
  4. Complex compounds with specific ligands have the ability to catalyze or stoichiometrically aid in the transition of molecules.

Double Salts

In aqueous solutions, double salts are totally ionizable, and each ion in the solution delivers the corresponding confirmatory test. Potash alum, for example, is a double sulfate. K2SO4 is the chemical formula. When Al2(SO4)3.24H2O is ionized, it produces K+, SO2-4, and Al+3 ions, which respond to the tests.

Coordination Complex

In aqueous solutions, coordinate complexes are only partially ionizable. These produce a complexion that isn’t completely ionized. Potassium Ferrocyanide is one example. [K4Fe(CN)6]. K+ and [Fe(CN)6]4- [ferro cyanide ions] are formed when it ionizes.

Applications of Coordination Compounds

Coordination compounds’ unique features, as explained in the previous chapter, make them particularly helpful in a variety of processes and industries. Some of these coordination compound applications are listed below.

  1. Because of the color of coordination compounds containing transition metals, they are widely employed in industries for material coloration. In the dye and pigment industries, they are used.
  2. In the electroplating process, some complex molecules using cyanide as a ligand are employed. These chemicals are also beneficial in the field of photography.
  3. Many metals can be extracted from their ores with the use of coordination complexes. Nickel and cobalt, for example, can be recovered from their ores via hydrometallurgical procedures using coordination complex ions.

Werner’s Theory of Coordination Compounds

Werner published a theory in 1893 that explained the structures, production, and nature of bonding in coordination molecules. This notion is known as Werner’s theory of coordination compounds. Werner was the first inorganic chemist to win the Nobel Prize in Chemistry, which he received in 1913. He looked into a variety of complicated chemicals that resulted from the reaction of cobalt chloride and ammonia.

Postulate of Werner’s Theory

There are two sorts of valencies in coordination compounds’ core metals: primary valency and secondary valency.

Primary Valency

The valencies that a metal exhibits in the production of simple salts are known as primary valencies. CoCl3, NaCl, CuSO4, and other salts are examples. In modern terms, it refers to a metal’s oxidation number. For example, in CoCl3, the primary valencies of Co are 3 and the oxidation state is +3. Similarly, the oxidation state of Na in NaCl is +1, while the oxidation state of Cu in CuSO4 is +2. Ionization is possible for the primary valencies. These are non-directional and do not provide any geometry to complicated compounds because they are written outside the coordination sphere. [Co(NH3)6]Cl3, oxidation state +3, number of primary valencies 3.

Secondary Valency

  1. Negative ions, neutral molecules, or both are used to provide metals secondary valency.
  2. In current terms, it refers to the metal’s coordination number.
  3. Secondary valencies are written within the coordinating sphere.
  4. These are directed in character and provide the complex a defined geometry.
  5. They aren’t ionized.

Limitations of Werner’s Theory

  1. It could not account for all elements’ failure to create coordination compounds.
  2. Werner’s coordination theory fails to explain the nature of the bonding between the core metal atom and the ligands.
  3. Werner’s coordination theory failed to describe complicated geometry when secondary valency was equal to 4.
  4. Werner’s hypothesis explains some of the features of coordination compounds, but it does not explain their color or magnetic properties.

Sample Problems

Question 1: What are the limitations of Werner’s theory?


Werner was unable to describe the coordinate compound’s colour. He couldn’t explain coordination compounds’ magnetic and optical properties.

Question 2: What is the primary valency according to Werner’s?


The valencies that a metal exhibits in the production of simple salts are known as primary valencies. It represents the metal’s oxidation condition. They’re ionisable and can be written outside of the coordination sphere.

Question 3: What applications and importance do coordination compounds have?


Plants, minerals, and other organisms contain coordination chemicals. They’re widely employed in the metallurgy and analytical chemistry industries. The following are some of the most important applications of coordination chemicals.

  1. To determine the hardness of water, coordination chemicals are utilised.
  2. Catalysts made of coordination compounds are used in a variety of industrial operations.
  3. In the extraction of metals such as gold and silver, coordination compounds are commonly used.
  4. Coordination molecules in chemistry are also important in biological systems. Chlorophyll (photosynthesis pigment) and magnesium coordination molecule, for example.

Question 4: What is a double salt?


In aqueous solutions, double salts are totally ionizable, and each ion in the solution delivers the corresponding confirmatory test.

Question 5: What is a co-ordination complex?


In aqueous solutions, coordinate complexes are only partially ionizable. These produce a complexion that isn’t completely ionised.

Question 6: How did Werner first explain bonding in complexes?


Werner was the first to propose proper structures for complex ion coordination compounds in which neutral or anionic ligands surround a core transition metal atom. Werner postulated the structure [Co(NH3)6]Cl3, which has the Co3+ ion at the vertices of an octahedron surrounded by six NH3.

Question 7: Why do coordination compounds have color?


When ligands form a coordination complex with a transition metal, electrons in the d orbitals split into high energy and low energy orbitals. In this process, some wavelengths are absorbed, subtractive colour mixing happens, and the coordination complex solution becomes coloured.

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Last Updated : 07 Feb, 2022
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