Important physical Properties
•there is Anomalous Configuration due to half filled and full filled d-orbitals and also due to the factors like Nuclear-electron & Electron-Electron forces.
Eg:- 2nd(Nb,Ru,Rh,Pd) ,3rd(Pt,Ir)
Atomic & Ionic Radii
Atomic radii Decreases gradually from yattrium to cadmium but from Ruthenium onwards it remains practically Constant or increases only Slightly toward the End.
•The atomic radii of transition metal of Second Series have larger values than those of first Series but atomic radii of third series & second Series is nearly same this is due to the lanthanide effect.
Lanthanoid Contraction:-The Steady decrease in atomic and ionic sizes of Lanthanide elements with increasing atomic number.
Cause of Lanthanoid contraction:-we know that 4f electrons shield each other from the nuclear charge Quite poorly because of diffused shape of f-orbitals.As a result ,with increase in atomic number ,effective nuclear charge experienced by each 4f-electron increases and whole of 4f-shell contracts at each sucessive element.
The Sum of successive reductions gives the total Lanthanoid Contraction.
Density Increases till Rh & Ir then it start decreasing due to the increased forces of repulsion between added electrons then the attractive force due to the increased nuclear charge.
•At. Size of 3rd and 2nd series remains same but atomic mass increases in case of 3rd Series ,it Results in Just doubled density then the Second Series.
Melting & Boiling points:-
are very high for transition elements and it Reach maximum value at group 7 or 8 then decreases with increase of atomic number.
The effect of Increasing nuclear charge is opposed by the additional Screening effect of the nucleus and consequently ionisation energy increases ,But Quite slowly Among a period of d-block elements.
All elements of 2nd and 3rd transition series have high density ,hardness, high melting and boiling points,high tensile strength, ductility, malleability, high thermal and electrical conductivity and lustre.
•Due to the Low Ionisation Energies and number of vacant orbitals in their atoms.
they exhibit higher coordination number and their higher oxidation states are more stable than the corresponding first Transition Series elements.
•+2,+3 oxidation states are less important for 2nd and 3rd T.Series.
there Reactivity is less than First Transition series.
The transition elements of first Series form mainly high Spin Complexes while those of 2nd And 3rd T.Series form low spin Complexes due to Less interelectronic Repulsion in 4d & 5d wrto 3d- Orbital.
•It has been observed that the magnetic moment is higher than calculated by Spin only .Because there is Contribution of orbital motion of electrons also.
•2nd and 3rd T.S. also shows Extensive Temp. Dependent Paramagnetism.
they have High Coordination number of 7 & 8 in their common complexes.
2nd & 3rd T.Series metals have Strong tendency to form metal-metal bonds in comparison to their respective Ist T.Series.
•Heavier elements are more prone to metal-metal bonding.
Comparative Study of 2nd and 3rd T.SERIES Elements.
Zirconium (Zr) and Hafnium(Hf)
Zr & Hf have larger atomic and ionic radii then Ti.
• their atomic radii are identical so as their chemical properties.
•only few compounds of oxidation state less than +4 exists.
•Coordination number of Zr and Hf is commonly 7 or 8 whereas Ti has 6 as maximum coordination number.
•Both form all the four tetrahalides.
•Aqueous Chemistry of Zr and Hf is not very extensive.
Niobium(Nb) and Tantalum(Ta)
They have highest oxidation state of +5 and their pentaoxides are more stable than that of vanadium and difficult to reduce.
•In oxidation state +2 and +3 metal-metal bonds are fairly common.
•Lower oxidation states are less stable and coloured while oxidation state +5 is colorless and more stable.
•They Form only few complexes, and spin pairing will be favoured in Nb and Ta . For eg. VCl4 is paramagnetic but NbCl4 is diamagnetic through Polymerisation and spin-spin intraction.
Molybdenum(Mo) & Tungsten(W)
•Mo ,W have similar size and chemical properties .
•+2 oxidation state is not known except for quadraply bonded Mo24+ units.
•they form large number of complexes in higher oxidation state.
•in lower oxidation state there is tendency to form metal-metal bonding as in Mo(iii) and W(iii) forming Mo2Cl93- ,W2Cl93- containing two MCl6 octahedral Sharing a face.
Technetium(Tc) and Rhenium(Re)
•Typical properties as in 2nd and 3rd T.Series .
•TCO4– & ReO4– are less oxidising agent than MnO4– and are stable in alkaline medium unlike MnO4–
•Tc & Re are mostly spin paired bcoz spin pairing is favoured due to Bigger sized d-orbitals and Higher Nuclear charge.
it includes Ruthanium (Ru) ,Osmium (Os) ,Rhodium(Rh),Iridium(Ir) ,Palladium (Pd) and Platinum(Pt).
•these are Rare Elements ,having Some common features but there are wide variations depending upon different stabilities of oxidation and Stereochemistry.
Ruthenium(Ru) & Osmium(Os)
•Has little Resemblance with Fe and in some complexes with π-bonding ligands (such as CO,PR3 ) Higher oxidation states are much more readily obtained than for Fe.
•Both Shows highest oxidation state of +8 and form yellow oxides of OsO4 ,RuO4–
Rhodium(Rh) and Iridium(Ir)
•Rh(vi) and Ir(vi) are known for their hexaflorides and fluorination of metal give tetrameric Penta floride , Rh4F20
•Rh(iv) is very stable state with RhO2,RhF4,RhF6–,RhCl62- etc.
•Na2[IrCl6] is common compound of irridium.
How Rh & Ir differ from Co(iii) complexes:
•On Reduction of trivalent complexes ,the Divalent complex is not obtained except under special conditions for Rh.
•Form Rh(i) ,Ir(i) planar four coordinate complexes and undergoes many oxidative addition rxn.
•Rh(iii) is difficult to oxidize and only few unstable compounds of Rh(iv) are known.
Palladium and platinium
•Principle oxidation states of Pd and Pt are +2 & +4 .
•M-M bond is involved in the chemistry of +1 & +3 states.
•PtCl4 is obtained as Red brown crystals by heating Chloroplatinic acid (H3O)2PtCl6 in chlorine.whereas PdCl4 does not exist.
•PdF2 is known but PtF2 is not Known.
•Platinum(ii) chloride in the presence of excess of chloride ions Forms PtCl42- .
also compounds like K[PtCl3(C2H4)] called Zeise Salt,[Pt(NH3)2Cl2] are known.
•Cis[Pt(NH3)2Cl2] is used in Chemotherapy for the Treatment of Cancer.
•Oxidation states +5 & +6 are found only in few fluoro Compounds.
Silver(Ag) and Gold (Au)
•Oxidation state +1 is most Common for Ag+ .
•Au3+ is present as Complexed Species in all Solution as anionic Species .
•Ag(ii) ,Ag(iii) ,Au(i) are unstable to water or exist in insoluble compounds or Complexed Species.
•Gold shows Six oxidation states from -1 to +3 and +5 .
Cadmium(Cd) and Mercury(Hg)
•Both Exhibit +2 oxidation State as Zn and have No Empty d-orbital and there is no dπ bonding in these as compared to the other d-block elements.
•All the three elements are known to exist in Univalent State as Dimers Zn22+ ,Cd22+,Hg22+ .
M-M bond Strength decreases as Zn22+< Cd22+< Hg22+
Organometallic compounds of mercury have been used in the preparation of organometallic Compounds of other metals.