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Werner was born in 1866 in Mulhouse, Alsace (which was then part of France, but which was annexed by Germany in 1871). He was raised as Roman Catholic.[3] He was the fourth and last child of Jean-Adam Werner, a foundry worker, and his second wife, Salom Jeannette Werner, who originated from a wealthy family.[3] He went to Switzerland to study chemistry at the Swiss Federal Institute (polytechnikum) in Zurich. Still, since this institute was not empowered to grant doctorates until 1909, Werner received a doctorate formally from the University of Zrich in 1890.[3] After postdoctoral study in Paris, he returned to the Swiss Federal Institute to teach (1892). In 1893 he moved to the University of Zurich, where he became a professor in 1895. In 1894 he became a Swiss citizen.[3]
In his last year, he suffered from a general, progressive, degenerative arteriosclerosis, especially of the brain, aggravated by years of excessive drinking and overwork. He died in a psychiatric hospital in Zrich.[3]
Before Werner, chemists defined the valence of an element as the number of its bonds without distinguishing different types of bonds. However, in complexes such as [Co(NH3)6]Cl3 for example, Werner considered that the Co-Cl bonds correspond to a "primary" valence of 3 at long distance, while the Co-NH3 bonds which correspond to a "secondary" or weaker valence of 6 at shorter length. This secondary valence of 6 he referred to as the coordination number which he defined as the number of molecules (here of NH3) directly linked to the central metal atom. In other complexes, he found coordination numbers of 4 or 8.
On these views, and other similar views, in 1904 Richard Abegg formulated what is now known as Abegg's rule which states that the difference between the maximum positive and negative valence of an element is frequently eight. This rule was used later in 1916 when Gilbert N. Lewis formulated the "octet rule" in his cubical atom theory.
In modern terminology, Werner's primary valence corresponds to the oxidation state, and his secondary valence is called coordination number. The Co-Cl bonds (in the above example) are now classed as ionic, and each Co-N bond is a coordinate covalent bond between the Lewis acid Co3+ and the Lewis base NH3.
CoCl3.5NH3 complex: The coordination number of cobalt in this compound is also 6, but the number of NH3 molecules is reduced to 5 from 6 and one remaining slot is now occupied by chloride ions. Because it has both primary and secondary valency, this chloride ion exhibits dual behavior. In the figure, the secondary valency is represented by a full line, while the main valency is represented by a dotted line.
CoCl3.4NH3 complex: Two chloride ions in this compound exhibit dual behavior, satisfying both Primary and Secondary Valencies. This compound will precipitate AgNO3, which corresponds to one Cl- ion, and the total number of ions, in this case is two. As a result, it can be written as [CoCl2(NH3)4]Cl.
CoCl3.3NH3 complex: In this molecule, three chloride ions satisfy primary and also secondary valency. At room temperature, silver nitrate does not precipitate Cl-. Hence, the complex compound behaves as a neutral non-conducting molecule. It may be written as [CoCl3(NH3)3].
[CoCl2(NH3)4]Cl: Werner stated that there are three theoretical structures for this complex. Planar, trigonal prisms and octahedral are examples. There are three possible isomers for a planar structure, three for a trigonal prism, and two for an octahedral structure.
Werner concluded that the geometrical arrangement of the coordinated group around the central atom in this compound was octahedral since only two isomers of the compound could be isolated. Werner was able to conclude that the six coordinated complexes have octahedral geometry in the case of various additional complexes in which the coordination number of the central atom was six.
Complex [PtCl2(NH3)2]: The coordination number of the metal in this complex is 4, and Werner discovered that it existed in two isomeric forms, cis and trans. This demonstrates that all four ligands are on the same plane. As a result, the structure should be square planar or tetrahedral.
Werner shifted his attention to the geometrical configurations of the coordinated groups. The central metal or metal atoms in coordination compounds have two forms of valency.The metal atom satisfies both its primary and secondary valencies.
Ans. The first compound has one ionisable chloride, whereas the second compound has no ionisable ion outside the coordination sphere. Electrical conductance is directly proportional to the number of ions in the solution. This is why the first compound has a higher electrical conductance than the second compound.
Alfred Werner, a Swiss chemist, in 1893 proposed his theory of coordination compounds which is also known as Werner's theory. This theory helped in explaining the structure and bonding in coordination compounds. The main postulates of Werner's theory of coordination compounds are as follows:
Primary valency (also known as ionizable valency) is satisfied by negative ions and is usually non-directional in nature. It indicates the oxidation state of the central metal ion. It's usually satisfied by anions.
Secondary valency (also known as coordination valency or non-ionizable valency) corresponds to the coordination number of the central ion, i.e., the number of ligands attached to the metal ion in the coordination sphere. These are usually satisfied by neutral molecules or ions. This type of valency is directional in nature.
Werner was the first inorganic chemist to be awarded the Nobel Prize for chemistry in 1913. He studied many complex compounds obtained from the reaction between cobalt chloride and ammonia.
The cryoscopic measurement (i.e., measurement of depression in freezing point) gives the number of ions formed by the dissociation of an ionic compound. The depression in freezing point is a colligative property and depends upon the number of particles in the solution. The greater the number of particles, the more will be the freezing point.
On the addition of silver nitrate solution, with chloride complex. The chloride ions which present outside the coordination sphere undergo precipitation reaction. As the number of chloride ions present outside the sphere increases, the number of formation of precipitates increases and vice versa.
In 1823, Werner put forth this theory to describe the structure and formation of complex compounds or coordination compounds. It is because of this theory that he got the Nobel prize and is known as the father of coordination chemistry. Are you ready to learn the important postulates of this theory?
1) CoCl3.6NH3 Complex: In this compound, the coordination number of cobalt is 6 and NH3 molecules satisfy all the 6 secondary valencies. Chloride ions satisfy the 3 primary valencies. These are non-directional in character. These chloride ions instantaneously precipitate on the addition of silver nitrate. The total number of ions, in this case, is 4, three chloride ions and one complex ion.
2) CoCl3.5NH3 complex: In this compound, cobalt has the coordination number of 6. However, we see that the number of NH3molecule decreases to 5. The chloride ion occupies the remaining one position. This chloride ion exhibits the dual behaviour as it has primary as well as secondary valency.
Werner turned his attention towards the geometrical arrangements of the coordinated groups around the central cation. He was successful in explaining the cause behind optical and geometrical isomerism of these compounds. Some examples are as follows:
1) [CoCl2(NH3)4]Cl complex: According to Werner, there are three structures possible for this complex. These are planar, trigonal prism, octahedral. The number of possible isomers is 3 for planar, 3 for trigonal prism and 2 for octahedral structure.
However, as we could isolate only two isomers of the compound, he concluded that geometrical arrangement of the coordinated group around the central atom in this compound was octahedral. In the case of several other complexes in which the coordination number of the central atom was six, Werner was of the opinion that in all these cases the six coordinated complex have octahedral geometry.
He also read the geometry of the complexes where the coordination number of the central metal atom is 4. He gave two possible structures for such compounds: Square Planar and Tetrahedral. Let us look at an example of the same.
2) [PtCl2(NH3)2] complex: In this complex, the coordination number of the metal is 4. According to Werner, this complex exists in two isomeric forms, cis and trans. This shows that all the four ligands lie in the same plane. Therefore, the structure should be a square planar or tetrahedral.
Werner's coordination theory from 1893 explained the structure and properties of transition metal complexes. It proposed that metals exhibit primary and secondary valences. Primary valency corresponds to oxidation state and is satisfied by anions, while secondary valency corresponds to coordination number and is satisfied by ligands. Werner's theory could successfully explain the structures of cobalt(III) and platinum(IV) ammine complexes based on these concepts. However, it had limitations and could not explain all properties of coordination compounds.Read less
According to Werner's theory, metal ions have two types of valency-primary and secondary, where the primary valency is said to be satisfied by negative ions only, and the secondary valency can be satisfied by positive ligand, negative or neutral molecule.
A certain number of ions, atoms or molecules closely associate around a central atom leading to the formation of distinct entity called coordination complex.The groups atoms or molecules linked to the central atom are said to be coordinated with the latter and their number gives the coordination number.
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