CHEMISTRY OF d-BLOCK ELEMENTS
 
 
 
d-Block Elements
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   The elements which have partially filled d-orbitals either ground state or in one or more of their ions, are    called d-block elements or outer transition elements. Their properties are intermediate between s-block    elements and p-block elements. They are more electropositive than p-block elements but less    electropositive than s-block elements. They form ionic compounds in their lower oxidation state and    covalent compounds in higher oxidation states. They are all metals and have electronic configuration
   ns2, (n-1)d1 to 10
General characteristics of d-block elements
Electronic configuration of first series of
d-block elements
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   For first series (Sc z=21) to (Zn z=30)
   Sc (z=21): 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d1.
   Ti (z=22) : 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d2.
   V (z=23) : 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d3.
   Cr (z=24) : 1s2, 2s2, 2p6, 3s2, 3p6, 4s1 , 3d5.
   Mn (z=25) : 1s2, 2s2, 2p6, 3s2, 3p6, 4s2 ,3d5.
   Fe (z=26) : 1s2, 2s2, 2p6, 3s2, 3p6, 4s2 ,3d6.
   Co (z=27) : 1s2, 2s2, 2p6, 3s2, 3p6, 4s2 ,3d7.
   Ni (z=28) : 1s2, 2s2, 2p6, 3s2, 3p6, 4s2 ,3d8.
   Cu (z=29) : 1s2, 2s2, 2p6, 3s2, 3p6, 4s1 ,3d10.
   Zn (z=30) : 1s2, 2s2, 2p6, 3s2, 3p6, 4s2 ,3d10.
Metallic character
   All transition elements are metals.
Atomic size
   The atomic size of d-block elements decreases from Sc to Zn due to increase in nuclear charge. Their    atomic sizes are smaller than that of s-block elements.
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Ionization potential
   The I.P. values of transition elements are intermediate between those of s-block and p-block elements.    This shows that they are more electropositive than p-block elements and less reactive than s-block    elements. Due to intermediate values I.P. they form ionic compounds as well as covalent compounds.
Oxidation states
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   Transition elements show variable state oxidation in their compounds. Reason of variable oxidation state    is that there is a very small energy difference in between (n-1)d and ns orbitals. As a result ,electrons    of (n-1)d orbitals as well as ns-orbitals take part in bond formation. Variation in oxidation state is related    to their electronic configuration.
   For example:-
   Ti : +2, +3, +4.
   Cr : +1, +2, +3, +4, +5, +6.
   Mn : +2, +3, +4, +6, +7.
   Fe : +2, +3.
   Cu : +1, +2.
Melting and boiling point
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   Melting and boiling point of these elements are very high (except Zn). These higher values are due to    small atomic radii of transition elements which provides greater inter atomic forces of attraction. They    are very hard .
Conductivity
   Transition elements are good conductor of heat and electricity.
Colour
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   Except zinc all the transition metals complex ions are colourless due to presence of unpaired electrons.    The colour of ions can be explained on the basis of "Crystal field theory". According to this theory ,the    bonding between ligands and a metal ion is electrostatic. The ligands surrounding the metal ion and
   create an electrostatic field around its d-orbitals. This field split '5' degenerated d-orbitals in to two
   sets of different energies.
   (i) A high energy pair (eg) of dx2-dy2 and dz2.
   (ii) A low energy trio (t2g) of dxy, dyz, dzx.
   In many cases difference of energy between two sets 'eg' and 't2g' is equivalent to a wavelength in the    visible region. Thus absorbing visible light, an electron may be able to move from lower energy set t2g to    higher energy set eg. In doing so, some of the component wavelength of white light is removed, so the    remaining component wavelength of light reflected or transmitted shows the colour.
   For example: Cu+2 (blue), V+3 (green), Co+2 (pink), Fe+2 (green), Fe+3 (yellow), Ti+3 (purple).
   At different oxidation states, same element produce different colours. www.citycollegiate.com
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