UNIT 8 THE d- AND f- BLOCK ELEMENTS
- The d-block consisting of Groups 3-12 occupies the large middle section of the periodic table. The elements of the inner-d orbitals are progressively filled in this section. The f-block is placed outside at the bottom of the periodic table and in the elements of this block, 4f and 5f orbitals are progressively filled.
- Corresponding to the filling of 3d, 4d and 5d orbitals, three series of transition elements are will recognized. All the transition elements exhibit typical metallic properties such as:
- High tensile strength
- Ductility
- Malleability
- Thermal and electrical conductivity
- Metallic character
- The melting and boiling points are high which are attributed to the involvement of (n-1)d electrons resulting into strong interatomic bonding. In many of these properties the maxima occurs at about the middle of each series which indicates that one unpaired electron per d orbital is particularly a favourable configuration for strong interatomic interaction.
- Successive ionization enthalpies do not increase as steeply as in the main group elements with increasing atomic number. Hence, the loss of variable number of electrons from (n-1)d orbitals is not energetically favourable. The involvement of (n-1)d electrons in the behaviour of transition elements impart certain distinct characteristics to these elements.
- In addition to variable oxidation states, they exhibit paramagnetic behaviour, catalytic properties and tendency for the formation of coloured ions, interstitial compounds and complexes.
- The transition elements vary widely in their chemical behaviour. Many of them are sufficiently electropositive to dissolve in mineral acids although a few are noble. Of the first series, with the exception of copper, all the metals are relatively reactive.
- The transition metals react with a number of non-metals like oxygen, nitrogen, sulphur and halogen to form binary compounds. The first series transition metal oxides are generally formed from the reaction of metals with oxygen at high temperatures. These oxides dissolve in acids and bases to form oxometallic salts.
- The two series of inner transition elements, lanthanoids and actinoids constitute the f-block of the periodic table. With the successive filling of the inner orbitals, 4f, there is a gradual decrease in the atomic and ionic sizes of the metals along the series (lanthanoids contraction).
- Lanthanum and all the lanthanoids are rather soft white metals. They react easily with water to give solutions giving +3 ions. The principal oxidation state is +3 although +4 and +2 oxidation states are also occasionally exhibited by some.
- The chemistry of the actinoids is more complex due to their ability to exist in different oxidation states. Also, many of the actinoids elements are radioactive which makes their study rather difficult.
- Applications of d-block and f-block elements:
- Steel
- Catalyst
- Complexes
- Organic synthesis