d block elements

 d block :

      Elements in which the last electron filled in the d-sub shell of the  penultimate shell is called d-block elements. Elements from group 3 to 12 (Transition elements) belong to d-block .

[The group number of d - block elements will be the same as the sum of the electrons in the outermost s subshell and the number electrons in the preceding d subshell, period number is same as the shell number of the outermost shell in the subshell electronic configuration]

Example: 

1. Scandium (21)

   Electronic configuration  

:1s2 2s2 2p6 3s2 3p6 4s 2 3d1

Block : d block 

Period  : 4

Group:1+2= 3

Peculiarity of the electronic configuration of chromium and copper

chromium(24) and copper(29) have 5 and10 electrons in the 3d orbitals is accepted rather than 4 and 9 electrons respectively . The reason is that full filled and exactly half filled orbitals have extra stability. Therefore to acquire more stability one electron of the 4s electron goes to the 3d orbitals. so that 3d orbital get half filled or completely filled in the chromium and copper respectively.

*d-block elements show variable oxidation state, why? 

The energy difference between the s subshell of the outermost shell and the d subshell of the penultimate shell in d block element is very small.Therefore during compound formation electrons from both these subshells may be transferred or shared.Hence these elements can show variable oxidation states. 

*s and p block elements show similarities in properties in their groups. But d block elements show similarity in a group as well as along a period.what might the reason be? 

The properties of elements are decided mainly by the electronic configuration in the outermost shell of their atoms.The s subshell of the outermost shell of the transition elements in a period has the same number of electrons. So d block elemets exhibit horizontal similarities. 

Oxidation states of d block elements:

 There is only a small difference of enegy between outermost s subshell and the penultimate d subshell of transition elements. Hence these elements can show variable oxidatio states. 

Oxidation states of Fe in ferrous chloride is +2

Oxidation states of Fe in ferric chloride is +3

•Two compounds formed by the combination of iron(Fe )and chlorine(Cl) 

i. Ferrous chloride  FeCl2

ii. Ferric chloride  FeCl3

a: Whih element shows different valencies? 

Ans. Fe

b: Does the metal atom of a compound gain or lose electrons? 

       Ans. Electron loses

c : How many electrons are given by Fe in the formation of FeCl2

       Ans. 2

d : In FeCl3 

      Ans.  3

e : The symbol of ions in each.

           

 Ferrous ion     Fe2+

  Ferric ion      Fe 3+

 f :sushell electronic configuration of 

 

Fe2+ and  Fe 3+

Asns:  Fe - 26  1s2, 2s2, 2p6 , 3s2, 3p6, 3d6, 4s2

            

        Fe2+   1s2, 2s2, 2p6 , 3s2, 3p6, 3d6

  

        Fe 3+  1s2, 2s2, 2p6, 3s2, 3p5 

g : During the formation of  Fe2+,the electron of 

which subshell is lost? 

      

Ans.  4s

h : Is only the electron of outermost subshell lost 

in  Fe 3+ ? Justify your answer? 

             

Ans.  No, 2 electrons are lost from the outer 4s level and one electron is lost from inner 3d level.

       In d block elements, the energy difference between the outer s - electron and inner d- electron is very low.So when  they take part in chemical reactions, s-electrons alone or d-electrons along with s-electrons may take part. Therefore these elements exhibit variable valencies. 

1• see the electronic cconfiguration of Cr -24 and Cu - 29 written by surya.

 Cr - 1s2 2s2 2p6 3s2 3p6 3d4 4s2

 Cu - 1s2 2s2 2p6 3s2 3p6 3d9 4s2

a : What is the wrong with these electron configurations? 

b : Write the correct electron configurations.

c : What is the reason for the change in electron configuration? 

Answer :

a : In the electron configuration of Cr,  4s contains only one electron and 3d contains 5 electrons.Similarly, in case of copper 4s contains 1 electron and 3d contains 10 electrons

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b : Cr - 1s2 2s2 2p6 3s2 3p6 3d5 4s1

 Cu - 1s2 2s2 2p6 3s2 3p6 3d10 4s1

c : The atom with half filled and full filled subshells have extra stability. By rearranging electrons, chromium gets half filled and copper gets full filled structure. So to get extra stability, the  electrons are re-arranged.

Activities :

2• Write the subshell electronic configuration of Fe2+ and Fe3+ ions(Z=26) 

3• when an atom loses electron, it is converted to ion.The ions of manganese are given below 

(i) Mn2+

(ii)Mn4+

(iii)Mn7+

a :How many electrons are lost by Mn during the formation of each of the ions? 

b :Write the subshell electron configuration of these ions.(Hint;atomic no.of Mn-25)

General properties of d block elements:

1. All transition elements are metals. 

2. Most of the d block elements form coloured compounds.(the colour of these ions is due to the presence of incomplete d subshell. A few of the transition elements  such as Cu+ ,Ag+,Sc3+ an Zn 2+ are colourless )

3.Transition elements act as catalyst. 

4. They form alloys

5d-block elements shows variableoxidation state. The common oxidation state of d-block elements are +2.  

6.d-block elements show horizontal similarity in properties.