Electronic Configurations Of The D Block Elements

Transition elements:
- Transition elements are those d-block elements which have partially filled d-orbitals in their atoms or in one of their common oxidation states.
- General definition: Elements of groups 3 to 12 (except Zn, Cd, Hg which have completely filled d-orbitals).
(i) Coloured compounds:
- Transition metal ions form coloured salts/complexes due to d–d electronic transitions.
- In the presence of ligands, the d-orbitals split into two sets of different energies (Crystal Field Splitting).
- Absorption of light promotes an electron from lower to higher d-orbital; the complementary colour is observed.
Examples: (blue), (purple).
(ii) Paramagnetic behaviour:
- Transition metals and their ions often contain unpaired d-electrons.
- Unpaired spins produce magnetic moments, giving paramagnetism.
- Paramagnetism is measured in Bohr magnetons (BM).
Examples: Fe ( , 4 unpaired e ), Mn ( , 5 unpaired e ).

The colour of transition metal ions arises due to d–d electronic transitions in partially filled d-orbitals.

Step 1: Analyze each ion.
- (A) Ni : Configuration = [Ar] 3d partially filled d-orbitals coloured.
- (B) Fe : Configuration = [Ar] 3d half-filled d-orbitals coloured.
- (C) Cu : Configuration = [Ar] 3d partially filled d-orbitals coloured.
- (D) Cu : Configuration = [Ar] 3d completely filled d-orbitals, no d–d transitions possible colourless.
Step 2: Final Answer.
Hence, the colourless ion is Cu .

Step 1: Recall electronic configuration of Mn.
Manganese ( ) has the electronic configuration:

Step 2: Possible oxidation states.
Manganese exhibits a wide range of oxidation states from +2 to +7, due to variable involvement of 3d and 4s electrons.

Step 3: Most common oxidation states.
- : This state arises from loss of 4s electrons. Example: MnCl . This is very common and stable.
- : This state arises from loss of 4s and two 3d electrons. Example: MnO . This is also very common in nature.
Other states (+5, +6, +7) exist but are less stable and less frequently encountered in common compounds. The highest oxidation state +7 is found in KMnO , but it is not as commonly occurring as +2 and +4.
Step 4: Final Answer.
Hence, the most common oxidation states of manganese are +2 and +4.

Step 1: Consider electronic configurations.
- Mn (Z = 25): [Ar] 3d 4s
- Mn : [Ar] 3d (stable half-filled configuration)
- Mn : [Ar] 3d (unstable, not half-filled)
Step 2: Stability explanation.
Mn has exactly half-filled 3d orbitals (3d ), which is particularly stable due to exchange energy and symmetrical distribution. On the other hand, Mn with 3d lacks this extra stability. Final Answer:

Transition metals form colored compounds due to the electronic transitions between their d-orbitals. The color is a result of these transitions when electrons move from one d-orbital to another under the influence of visible light.
- In transition metals, the d-orbitals are split into two energy levels under the influence of a ligand field. When light is absorbed, electrons are excited from lower to higher energy d-orbitals, and the energy corresponding to the absorbed light corresponds to the color observed in the complex. This is why many transition metal compounds, like those of copper, chromium, and cobalt, show distinct colors.