4.5 Transition Elements
Elements located in the d-block (Group 3 to 12) of the periodic table are known as transition elements. These elements exhibit several characteristic properties that distinguish them from other elements.
1. High Density
Transition elements generally possess high densities due to their higher atomic masses and closely packed structures. For example:
- Iron (Fe) has a density of 7.87 g/cm³.
- Tungsten (W) has a density of 19.3 g/cm³.
2. High Melting Points
Transition elements have high melting points due to their strong metallic bonding, which arises from the presence of partially filled d-sub shells. For example:
- Tungsten (W) has a melting point of 3422°C.
- Platinum (Pt) has a melting point of 1768°C.
3. Variable Oxidation States
Transition elements exhibit multiple oxidation states because their d-sub shell can also participate in bonding along with the s-sub shell. For example:
- Iron (Fe) has oxidation states +2 and +3.
- Copper (Cu) has oxidation states +1 and +2.
4. Coloured Compounds
Transition elements often form vibrant colored compounds. For example:
- Copper compounds appear blue or green.
- Chromium compounds are often red or green.
5. Catalysts for Industrial Processes
Transition metals and their compounds are widely used as catalysts in various industrial processes. For example:
- Iron is used in the Haber Process for the synthesis of ammonia.
- Platinum and palladium are used as catalysts in catalytic converters to reduce harmful emissions in automobiles and industrial units.
- Nickel is used as a catalyst in the manufacture of margarine.
- Platinum is used as a catalyst in the contact process for the manufacture of sulfuric acid.