Questions
5–8 MCQs per paper
Difficulty
Medium
Importance
High yield for JEE Main and NEET
Overview
The d- and f-block elements represent the transition and inner transition metals, characterized by the progressive filling of d- and f-orbitals. Mastering this topic is crucial for entrance exams as it integrates electronic configurations, oxidation states, and coordination chemistry, forming the basis for high-weightage inorganic chemistry questions.
General Properties of Transition Metals
Transition elements exhibit metallic character, high melting points, and variable oxidation states due to the participation of (n-1)d electrons. Their atomic radii decrease across a series but remain relatively constant after the middle due to the shielding effect of d-electrons.
- High atomization enthalpy due to strong interatomic metallic bonding
- Variable oxidation states arise from small energy gap between ns and (n-1)d orbitals
- Paramagnetism increases up to group 7 and then decreases
- Ionic radii decrease across a series (Lanthanoid contraction impacts d-series)
Oxidation States and Stability
Transition metals show a wide range of oxidation states, with the most stable states often linked to half-filled or fully-filled d-orbitals. Understanding the relative stability of ions in aqueous solutions requires looking at electrode potentials (E°) rather than just sublimation or ionization energy.
- Mn exhibits highest oxidation state of +7 in KMnO4
- Stability of +2 state increases across the series for M2+/M
- E°(M2+/M) values are negative except for Cu (+0.34V)
- Cr2+ is a strong reducing agent (d4 to d3 configuration)
Coloured Compounds and Magnetic Moments
The color of transition metal ions arises from d-d transitions, which occur when electrons absorb energy to move between split d-orbitals. Magnetic behavior is typically calculated using the 'spin-only' formula, which is a standard quantitative question type in JEE/NEET.
- Color is observed when d-orbitals are partially filled
- Spin-only magnetic moment formula: μ = sqrt(n(n+2)) BM
- d0 and d10 systems are colorless (e.g., Sc3+, Zn2+)
- Magnetic moment increases with the number of unpaired electrons (n)
Lanthanides and Actinides
Lanthanoids exhibit a steady decrease in atomic/ionic size known as lanthanoid contraction, which influences the properties of subsequent 4d and 5d series elements. Actinides show a greater range of oxidation states compared to lanthanoids due to comparable energies of 5f, 6d, and 7s orbitals.
- Lanthanoid contraction causes similarity in size between Zr and Hf
- Common oxidation state for lanthanoids is +3
- Actinides exhibit +3, +4, +5, +6, and +7 oxidation states
- 4f electrons have poorer shielding than d-electrons
Formula Sheet
Magnetic moment μ = sqrt(n(n+2)) BM
Effective Nuclear Charge Zeff = Z - σ
E°cell = E°cathode - E°anode
Exam Tip
Always check the electronic configuration of Cr and Cu exceptions first before calculating oxidation states or magnetic moments.
Common Mistakes
- Confusing paramagnetic character with the presence of any d-electron rather than counting unpaired electrons specifically.
- Neglecting the effect of Lanthanoid contraction when comparing atomic sizes of 4d and 5d transition series.
- Assuming all colored compounds are due to d-d transitions, while ignoring charge transfer spectra in compounds like KMnO4.
More Revision Notes
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