d-Block Properties — Chemistry Mnemonic
Target: mnemonic for d block transition metal properties chemistry
Why is this hard to memorize?
Transition metals (d-block, Groups 3-12) have unique properties due to partially filled d-orbitals: variable oxidation states, coloured compounds, catalytic activity, complex formation, and magnetic properties. NEET and JEE test: electronic configurations (exceptions for Cr and Cu), highest oxidation state trends, why compounds are coloured (d-d transitions), paramagnetism (unpaired electrons), and specific compounds like KMnO₄, K₂Cr₂O₇. Understanding the connection between electronic configuration and properties is key.
Classic mnemonics you should know
"Cr = [Ar]3d⁵4s¹ (not 3d⁴4s²). Cu = [Ar]3d¹⁰4s¹ (not 3d⁹4s²). "Half-filled and fully-filled d are extra stable""
Cr and Cu are exceptions to the Aufbau order: Cr adopts 3d⁵4s¹ because half-filled d⁵ is extra stable (exchange energy). Cu adopts 3d¹⁰4s¹ because fully-filled d¹⁰ is extra stable. These two exceptions are asked in almost every exam.
"Partially filled d-orbitals → d-d transitions → absorb visible light → appear coloured. d⁰ and d¹⁰ = colourless!"
When ligands surround a transition metal, d-orbitals split into two energy levels (crystal field theory). Electrons absorb visible light to jump between levels (d-d transition). The colour we see is the complementary colour of what's absorbed. d⁰ (Sc³⁺, Ti⁴⁺) and d¹⁰ (Cu⁺, Zn²⁺) have no d-d transitions → colourless.
"Variable oxidation states → can shuttle electrons → act as catalysts. Fe(Haber), V₂O₅(Contact), Pt(hydrogenation), MnO₂(decomposition)"
Transition metals are excellent catalysts because they can exist in multiple oxidation states, allowing them to transfer electrons to and from reactants. They also provide suitable surface for adsorption of reactants. Key examples: Fe in Haber process, V₂O₅ in Contact process, Ni in hydrogenation.
The complete list
- Variable oxidation states (d-electrons participate)
- Coloured compounds (d-d transitions)
- Catalytic activity (multiple oxidation states)
- Complex formation (empty d-orbitals accept lone pairs)
- Magnetic properties (unpaired d-electrons)
- Cr = [Ar]3d⁵4s¹ (exception)
- Cu = [Ar]3d¹⁰4s¹ (exception)
- Highest OS increases to Mn, then decreases
Frequently asked questions
Why do Cr and Cu have exceptional electronic configurations?
Due to extra stability of half-filled (d⁵) and fully-filled (d¹⁰) d-subshells. This stability comes from: (1) Maximum exchange energy — electrons with parallel spins in degenerate orbitals have extra stabilization. (2) Symmetrical distribution of electrons. In Cr, 3d⁵4s¹ has higher exchange energy than 3d⁴4s². In Cu, 3d¹⁰4s¹ is more stable than 3d⁹4s². The 4s→3d promotion costs less energy than the exchange energy gained.
Why are d⁰ and d¹⁰ compounds colourless?
Colour in transition metal compounds comes from d-d transitions: an electron absorbs visible light to jump from a lower d-orbital to a higher one (split by crystal field). In d⁰ (like TiO₂, Sc³⁺), there are no d-electrons to transition. In d¹⁰ (like ZnSO₄, Cu₂O), all d-orbitals are full — no empty orbital for the electron to jump into. No transition possible → no absorption → colourless.
Why does the highest oxidation state increase up to Mn and then decrease?
From Sc(+3) to Mn(+7), each element can use all its d-electrons plus 2 s-electrons for bonding: Ti(+4), V(+5), Cr(+6), Mn(+7). After Mn, the increasing nuclear charge holds d-electrons tighter — it becomes harder to remove them. Also, the d-electrons start pairing up, and paired electrons are harder to involve in bonding. So Fe max is +6 (rare), Co/Ni are mostly +2/+3, Cu is +1/+2.
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