Write the factors which are related to the colour of transition metal ions.

Explain the following : (i) Most of the transition elements show variable oxidation states. (ii) Most of the compounds of transition elements are coloured. (iii) Many transition elements and their compounds are paramagnetic .

(a) Define transition elements. Give the general electronic configuration of the transition elements. (b) (i) Name a transition element which does not exhibit variable oxidation state. (ii) Which of the 3d series of transition metals exhibit the largest number of oxidation states? (iii) Give reason why HCl is not used to acidify KMnO_4 solution in volumetric determination of Fe^(2+)

The IUPAC definition of a transition element is that it is an element that has an incomplete d-subshell in either the neutral atom or its ion. Thus the group 12 elements are member of the d-block but are not transition elements. Chemically solft members of the d-block occurs as sulphide minerals and are partially oxidised to obtain the metal, the more electropositive 'hard' metals occurs as oxides and are extracted by reduction. Opposite to p-block elements, the higher oxidation states are favoured by the heavier elements of d-block Metals on the right of the d-block tend to exist in low oxidation states and form complexes with the ligands. Square-planar complexes are common for the platinum metals and gold in oxidation states that yield d^8 electronic configuration, which include RH(I),Ir(I),Pd(II),Pt(II) and Au(III). The most distinctive features/properties of transition metal complex is their wide range of colours.The crystal field theory attributes the colour of the coordination compounds to d-d transition of the electron.It is important to note that (a) in absence of ligand, crystal field spilling does not occur and hence the substances is colourless, (b) the type of ligand also influences the colour of the complexes. Which of the following has dsp^2 hybridisation and is diamagnetic in nature ? (i) Na_4[Cr(CO)_4] , (ii) [Ni(DMGH)_2] , (iii) [PtHBr(PEt_3)_2] (iv) [As(SCN)_4]^(3-) , (v) [AuBr_4]^(-)

The transition element ( with few exceptions ) show a large number of oxidation states . The various oxidation states are related to the electronic configuration of their atoms. The variable oxidation states of a transition metal is due to the involvement of (n-1)d and outer ns electrons . For the first five elements of 3d transition series , the minimum oxidation state is equal to the number of electrons in 4s shell and the maximum oxidation state is equal to the sum of 4s and 3d electrons. The relative stability of various oxidation states of a given element can be explained on the basis of stability of d^(0),d^(5) and d^(10) configuration . In 3d series, the maximum oxidation state is shown by

The transition element ( with few exceptions ) show a large number of oxidation states . The various oxidation states are related to the electronic configuration of their atoms. The variable oxidation states of a transition metal is due to the involvement of (n-1)d and outer ns electrons . For the first five elements of 3d transition series , the minimum oxidation state is equal to the number of electrons in 4s shell and the maximum oxidation state is equal to the sum of 4s and 3d electrons. The relative stability of various oxidation states of a given element can be explained on the basis of stability of d^(0),d^(5) and d^(10) configuration . In which of the following pairs , the first species is more stable than second one

The transition element ( with few exceptions ) show a large number of oxidation states . The various oxidation states are related to the electronic configuration of their atoms. The variable oxidation states of a transition metal is due to the involvement of (n-1)d and outer ns electrons . For the first five elements of 3d transition series , the minimum oxidation state is equal to the number of electrons in 4s shell and the maximum oxidation state is equal to the sum of 4s and 3d electrons. The relative stability of various oxidation states of a given element can be explained on the basis of stability of d^(0),d^(5) and d^(10) configuration . Identify the correct statement