d and f Block Elements
2.0 Occurrence and General Characteristics of Transition Elements
2.0 Occurrence and General Characteristics of Transition Elements
Occurrence:
- Soft Metals of $d$-block elements are found in the form of sulfide where as hard in the form of Oxides. These metals on reduction produce free metals.
- Titanium is found in small quantities in coal, clay and sand.
- Vanadium is observed as vanadates of Zinc, Copper & Lead.
- Chromium is found as Chromite ($FeO.C{r_2}{O_3}$), Chrome Ochre ($C{r_2}{O_3}$), Crocosite ($PbCr{O_4}$).
- The Ore of Manganese is Pyrolusite ($Mn{O_2}$).
- Iron is found in free and combined states and its occurrence is next to aluminum.
- Cobalt is associated with nickel arsenic.
- Nickel is generally associated with cobalt.
- The important ores of copper are cuprite ($C{u_2}O$), Malachite ($CuC{O_3},{\text{ Cu(OH}}{{\text{)}}_2}$), azurite ($2CuC{O_3},{\text{ Cu(OH}}{{\text{)}}_2}$).
- Zinc is found with silver, copper, lead and platinum.
General Characteristics:
- Most of these metals are malleable, ductile and lustrous.
- They have high density, Melting point, Boiling point due to involvement of more number of electrons from $(n-1)d$ and $ns$ orbitals in metallic bonding.
- They are good conductors of heat and electricity and form large number of complexes.
- They exibit variable oxidations states as $(n-1)d$ and $ns$ electrons involved in bonding.
- Most of the cations have unpaired electrons.
- Transition Metals and their compounds have catalytic property.
- They form organometallic compounds.
- Due to increase in nuclear charge densities of these metals increases from left to right.
- Their ionization enthalpy increases with atomic number and decreases with size.
