Characteristic properties of Transition Elements:
1. All the transition elements are metals.
2. All these elements contain incompletely field inner p-orbital.
3. Oxidation states: Transition elements have variable oxidation states and show variable valency. It is due to the involvment of electrons in the inner d-orbital
Fe++(ous) → 3d5 Cr++ → 3d4 Mn++ → 3d5
Fe12(ic) → 3d5 Cr+3(ic) → 3d3 Mn+3 → 3d4
Lower oxidation states are generally more stable for 1st transition (-3d series)
4. Melting point: Transition metals have high melting points.
5. Atomic and Ionic radii: The outermost electronic configuration in (n - 1) dx ns2 the new comer electron is added to the (n - 1) du orbital while NSL and orbitals remain unchanged. Thus due to d-block contract on atomic and ionic radii in a series show very little variation.
6. Ionisation Potential: As variation in the atomic radii is very small, the variation in ionisation potential is also small. The ionisation potentials are practically constant in a transition metal series.
7. Colour salts (compound): Transition metals form salts e.g.
Fe++ salts → green
Fe+8 salts → yellow
Mn+2 salt → pink
Co+ salts → pink
The colour is due to either d-d transition or charge transfer.
8. Catalytic properties: Transition metals are good catalic agents e.g. finely divided nickel, platinised asbestos, paladium, iron etc. are used as catalysts.
9. Magnetic properties: Transition metals, free ions and salts of lower oxidation states are paramagnetic due to the presence of unpaired electrons.
Fe, Co and Ni are very strongly paramagnetic and are called as Ferromagnetic.
Para-magnetism is expressed as:
μ = √{n(n + 2)}
where μ = Magnetic moment. (Magnetic dipole moment)
n = number of unpaired electrons
The value of magnetic moment is expressed by the unit Bohr magnetion (B.M.)
Example: Cr++ : 3d4 →
Cr++ has 4d unpaired electrons, hence its will be = √{24} = 4.90 Mn (VIII) has 3d0 hence its μ value is zero, Mn (VIII) is diamagnetic.
Now it can be shown from the quantum theory of atoms and ions that the magnetic moment due to unpaired electrons in the atom or in the atom or iron is given by
μ = 2√{s(s + 1)} where s equals the sum of the spins of all the unpaired electrons that is n x 1/2
| Number of unpaired electrons |
S |
μ(B.M) |
| 1 |
1/2 |
1.73 |
| 2 |
1 |
2.83 |
| 3 |
3/2 |
3.87 |
| 4 |
2 |
4.90 |
| 5 |
5/2 |
5.90 |
10. Hydrolysis salts: Salts of transition metals are readily hydrolysed in aq. solution.
e.g FeCl3 + 3H2O → Fe(OH)3 + 3HCl
Aq. solution of salts of transition metals are acidic. Transition metal cations are associated with some convinient characteristics due to the presence of incompletely filled 'd' orbitals.
Due to high charge density, the cation of a transition metal pulls ions pair of electron from oxygen atom in H2O molecule and a hydrate finally gets hydrolysed.
e.g. Fe+3 + H2O → (H2O : Fe+2) → Fe(OH)+2 + H+
11. Complex formation: Transition metals have a great tendency to form complex compounds (co-ordination compounds). This tendency is due to the presence of incompletely filled 'd' orbitals and high effective nuclear charge (transition metals have low atomic volume). Transition metals and their cations can readily accept lone pair of electrons from ligands like NH3, CN-, H2O etc.
e.g. K4[Fe(CN)6] → [Fe(CN)6]-4 → octahedral
[Co(NH)6]Cl3 → [Co(NH3)+4] → octahedral
K2[Ni(CN)4] → [Ni(CN)4]-2 → square planar
Ni(CO)4 → Tetrahedral
[Ni(H2O)6]+2 → octahedral
