The d-block elements (transition metals) have several general properties that distinguish them from s- and p-block elements. Here’s a clear summary:
1. Variable Oxidation States
- Most d-block elements can show more than one oxidation state, usually differing by 1.
- This is because both the (n-1)d and ns electrons can participate in bonding.
- Example: Iron (Fe) shows +2 and +3; Copper (Cu) shows +1 and +2.
2. Formation of Colored Compounds
- Many d-block elements form colored ions and compounds.
- The color arises due to d–d electron transitions when light is absorbed.
- Example: [Cu(H₂O)₆]²⁺ is blue, [Ni(H₂O)₆]²⁺ is green.
3. Complex Formation
- d-block elements easily form coordination compounds (complexes) with ligands.
- Example: [Fe(CN)₆]³⁻, [Cu(NH₃)₄]²⁺.
4. Magnetic Properties
- Many d-block elements and their compounds are paramagnetic due to unpaired d-electrons.
- Example: Fe³⁺ has 5 unpaired electrons and is strongly paramagnetic.
5. Metallic Properties
- They are good conductors of heat and electricity, malleable, and ductile.
- They have high melting and boiling points (except for a few like Mercury).
6. High Density
- Most d-block elements have high densities, due to closely packed atoms and partially filled d-orbitals.
7. Catalytic Properties
- Many act as catalysts in chemical reactions, due to their ability to change oxidation states.
- Example: Fe in Haber process, Ni in hydrogenation reactions.
8. Formation of Alloys
- d-block metals often form alloys because of their similar atomic sizes and metallic bonding.
- Example: Steel (Fe + C), Brass (Cu + Zn).
9. Hardness
- Most d-block metals are hard and strong because of metallic bonding involving d-electrons.