The general electronic configuration of d-block elements is (n-1) d1-10 ns0-2, where n is the outer most shell.
General trends in the chemistry of transition elements.
Nearly all the transition elements display typical metallic properties such as high tensile strength, ductility, malleability, high thermal and electrical conductivity and metallic lustre. With the exceptions of Zn, Cd, Hg and Mn, they have one or more typical metallic structures at normal temperatures.
The transition elements (with the exception of Zn, Cd and Hg) are very much hard and have low volatility.
Melting and boiling points :
The melting and boiling points of the transition series elements are gernerally very high.
The atomic volumes of the transition elements are low compared with the elements of group 1 and 2. This is because the increased nuclear charge is poorly screened the transition metals are high.
Most o f transition elements show variable oxidation states. Participation of inner (n - 1 ) d-electrons in addition to outer ns-electrons because, the energies of the ns and (n - 1) d-subshells are nearly same.
Standard electrode potentials: The value of ionisation enthalpies gives information regarding the thermodynamic stability of the transition metal compounds in different oxidation states. Smaller the ionisation enthalpy of the metal, the stable is its compound.
Electrode potentials: In addition to ionisation enthalpy, the other factors such as enthalpy of sublimation, hydration enthalpy, ionisation enthalpy etc. determine the stability of a particular oxidation state in solution. The overall energy change is
The smaller the values of total energy change for a particular oxidation state in aqueous solution, greater will be the stability of that oxidation state. The electrode potentials are a measure of total energy change. Qualitative, the stability of the transition metal ions in different oxidation states can be determined on the basis of electrode potential data. The lower the electrode potential i.e., more negative the standard reduction potential of the electrode, the more stable is the oxidation state of the transition metal in the aqueous solution.
Thermochemical data (kJ mol-1) for the first row Transition Elements and the Standard Electrode potentials for the Reduction of M" to M
Formation of Coloured Ions : Most of the compounds of transition metals are coloured in the solid form or solution form. The colour of the compounds o f transition metals may be attributed to the presence of incomplete (n - 1) d-subshell.
The excess of other colours constituting white light are transmitted and the compound appears coloured. The observed colour of a substance is always complementary colour of the colour which is absorbed by the substance.
Magnetic Properties :
(i) Paramagnetic substances : The substances which are attracted by magnetic field are called paramagnetic substances.
(ii) Diamagnetic substances : The substances which are repelled by magnetic field are called diamagnetic substances. The ‘spin only’ magnetic moment can be calculated from the relation :
where n is the number of unpaired electrons and p is magnetic moment in Bohr magneton (BM) units.
The paramagnetism first increases in any transition series and than decreases. The maximum paramagnetism is observed around the middle of the series (as contains maximum number of unpaired electrons).
Formation of Interstitial Compounds : Transition metals form intersitial compounds with elements such as hydrogen, boron, carbon and nitrogen.
Catalytic properties: Many transition metals and their compounds act as good catalysts for various reactions. Of these, the use of Fe, Co, Ni, V, Cr, Mn, Pt, etc. are very common.
Alloy Formation : Alloys are hard, have high melting points and are more resistant to corrosion than parent metals.
d-BLOCK METAL COMPOUNDS :
1. Hydrated Ferrous Sulphate (FeSO4. 7H2O), Ferric chloride (FeCI3) and iron (III) oxide (Fe2O3)
2. Hydrated copper sulphur (CuSO4,5H2O) :
3. Silver nitrate (AgNO3):
4. Potassium permanganate (KMnO4) :
5. Potassium dichromate (K2CrO7) :