General Properties of Transition Metals Class 12 Chemistry | The d- and f-Block Elements

Understand it

The small energy difference between ns and (n-1)d orbitals allows different numbers of electrons to participate in bonding. Partially filled d-orbitals cause d-d transitions responsible for many colours, unpaired electrons cause paramagnetism, and vacant or suitable d-orbitals support complex formation. Their similar atomic sizes and metallic bonding also favour alloy formation.

Example

Fe shows +2 and +3 oxidation states, Cu²⁺ salts are often coloured, Ni forms complexes such as [Ni(CN)4]2-, and finely divided iron acts as a catalyst in the Haber process.

Rule to remember

Property-cause pattern: variable oxidation state arises from comparable ns and (n-1)d energies; paramagnetism depends on unpaired electrons; colour generally requires partially filled d-orbitals; complex formation is favoured by small size, charge, and available orbitals.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

Explain why Ti³⁺ is coloured but Sc³⁺ is colourless.

1Ti³⁺ has 3d1 configuration, so d-d transition is possible.
2Sc³⁺ has 3d0 configuration, so no d-d transition occurs and it is colourless.

Method you can reuse

For any property question, write the ion's d-electron count, check unpaired electrons or incomplete d-orbitals, then connect the observation to the correct cause and example.

Visual tip

A comparison table linking property, cause, and example is more useful than a structural diagram for this concept.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why do many transition-metal ions show colour?

Think first, then show answer

Many transition-metal ions have partially filled d-orbitals. Absorption of visible light can promote d-electrons between split d-levels, and the transmitted or reflected complementary colour is observed.

Common wrong answer

A realistic wrong answer is claiming all transition-metal ions are coloured. d0 and d10 ions are generally colourless because d-d transitions are not possible in the usual sense.

Don't mix this up

Students often give one reason for all properties. Colour is mainly linked to d-d transition in partly filled d-orbitals, while paramagnetism is linked to unpaired electrons. These are related but not identical explanations.

Exam tip

In reason-based answers, pair each property with its cause: variable oxidation state with ns and d-electron participation, colour with d-d transition, magnetism with unpaired electrons, and catalysis with variable oxidation state or surface adsorption.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

CBSE questions often ask for reasons for colour, magnetic nature, variable oxidation states, alloy formation, or catalytic behaviour, usually with a named ion or metal.

1
Enough for 1 mark
Transition metals show characteristic properties such as variable oxidation states, coloured ions, paramagnetism, complex formation, catalytic activity, high enthalpy of atomisation, high melting points, and alloy formation due to involvement of d-electrons.
2
Add for 2 marks
Example: Fe shows +2 and +3 oxidation states, Cu²⁺ salts are often coloured, Ni forms complexes such as [Ni(CN)4]2-, and finely divided iron acts as a catalyst in the Haber process.
3
Add for 3 marks
The small energy difference between ns and (n-1)d orbitals allows different numbers of electrons to participate in bonding.

Use the concept graph around this idea instead of revising it in isolation.

Position of d-Block Elements in the Periodic Table

d-block elements are elements in which the differentiating electron enters the d-subshell of the penultimate shell. They are placed between the s-block and p-block elements in the periodic table.

Magnetic Properties and the Spin-Only Formula

Magnetic behaviour of transition-metal ions depends mainly on the number of unpaired electrons. Paramagnetic species have unpaired electrons, while diamagnetic species have all electrons paired.

Preparation and Oxidising Properties of KMnO4 and K2Cr2O7

Potassium permanganate and potassium dichromate are important transition-metal compounds used as strong oxidising agents, especially in acidic medium. Their reactions involve reduction of Mn(VII) or Cr(VI) to lower oxidation states.

Trends in Atomic and Ionic Radii

Across a transition series, atomic and ionic radii generally decrease at first due to increasing nuclear charge, but the decrease becomes small because added d-electrons shield each other poorly. In f-block elements, poor shielding by f-electrons causes lanthanoid contraction.

Previous: Position of d-Block Elements in the Periodic Table Next: Trends in Atomic and Ionic Radii Back to full mind map

General Properties of Transition Metals

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General Properties of Transition Metals

Understand it

See it worked out

Check yourself

Write it in the exam

Related concepts

Practice this concept with focused MCQs

Help improve this page