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Most of the transition elements exhibit several oxidation states i.e., they show variable valency in their compounds. Some common oxidation states of the first transition series elements are given below in table,
Outer Ele. Confi. and O. S. for 3d- elements
Elements |
Outer electronic configuration |
Oxidation states |
Sc |
3d1 4s2 |
+ 2, + 3 |
Ti |
3d2 4s2 |
+ 2, + 3, + 4 |
V |
3d3 4s2 |
+ 2,+ 3,+ 4,+ 5 |
Cr |
3d5 4s1 |
+ 1, + 2, + 3, + 4, + 5, + 6 |
Mn |
3d54s2 |
+ 2, + 3, + 4, + 5, + 6, + 7 |
Fe |
3d64s2 |
+ 2, + 3, + 4, + 5, + 6 |
Co |
3d74s2 |
+ 2, + 3, + 4 |
Ni |
3d84s2 |
+ 2, + 3, + 4 |
Cu |
3d104s1 |
+ 1,+ 2 |
Zn |
3d104s2 |
+ 2 |
The relative stability of the different oxidation states depends upon the factors such as, electronic configuration, nature of bonding, stoichiometry, lattice energies and solvation energies. The highest oxidation states are found in fluorides and oxides because fluorine and oxygen are the most electronegative elements. The highest oxidation state shown by any transition metal is eight. The oxidation state of eight is shown by Ru and Os.
An examination of the common oxidation states reveals the following conclusions.
(i) The variable oxidation states shown by the transition elements are due to the participation of outer ns and inner (n–1)d-electrons in bonding.
(ii) Except scandium, the most common oxidation state shown by the elements of first transition series is +2. This oxidation state arises from the loss of two 4s electrons. This means that after scandium, d-orbitals become more stable than the s-orbital.
(iii) The highest oxidation states are observed in fluorides and oxides. The highest oxidation state shown by any transition elements (by Ru and Os) is 8.
(iv) The transition elements in the + 2 and + 3 oxidation states mostly form ionic bonds. In compounds of the higher oxidation states (compound formed with fluorine or oxygen), the bonds are essentially covalent. For example, in permanganate ion MnO4–, all bonds formed between manganese and oxygen are covalent.
(v) Within a group, the maximum oxidation state increases with atomic number. For example, iron shown the common oxidation state of + 2 and + 3, but ruthenium and osmium in the same group form compounds in the + 4, + 6 and + 8 oxidation states.
(vi) Transition metals also form compounds in low oxidation states such as +1 and 0. For example, nickle in, nickel tetracarbonyl, Ni(CO)4 has zero oxidation state. Similarly Fe in Fe(CO)5
has zero oxidation state.
The bonding in the compounds of transition metals in low oxidation states is not always very simple.
Example 1: The highest oxidation state of
Cr will be
(a) 2
(b) 3
(c) 4
(d) 6
Ans: d
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