p-Block, d-Block and f-Block Elements
Domain 8: p-Block, d-Block and f-Block Elements
This domain tests periodic trends and the characteristic chemistry of groups 15–18, transition metals, lanthanoids, and actinoids.
Core rules
- p-Block: down a group, atomic radius increases, ionisation enthalpy decreases, and metallic character increases. N, O, F show anomalous behaviour from small size and high electronegativity. Oxoacids strengthen with more oxygen and higher central oxidation state (HClO4 is strongest of the chlorine oxoacids).
- Group 15: NH3 basic, HNO3 strong oxidant; group 16: O2 paramagnetic, ozone bent; group 17: halogens are oxidising, F2 strongest; group 18: noble gases mostly inert, Xe forms fluorides and oxides.
- d-Block: variable oxidation states, coloured ions, paramagnetism, catalytic activity, alloy formation. Zn is not a typical transition metal because its d subshell is full in the atom and Zn2+ is d10.
- Transition-metal colour arises from d–d transitions; ions with d0 or d10 are usually colourless. Spin-only magnetic moment μ=√(n(n+2)) BM.
- f-Block: lanthanoid contraction causes a slow radius decrease; +3 state dominates. Actinoids show wider oxidation states and radioactivity.
Worked example
Fe3+ is d5. In a high-spin complex, all five d orbitals carry one unpaired electron, n=5. μ=√(5 x 7)=√35=5.92 BM. A low-spin d5 complex would have one unpaired electron and μ=1.73 BM, so magnetic data distinguish the two cases.
Traps
- Assuming every d-block element is a transition metal.
- Thinking the highest oxidation state always equals the group number; exceptions occur.
- Forgetting the inert-pair effect in heavy p-block elements.
- Predicting colour for d0/d10 ions.
- Confusing lanthanoid contraction with actinoid contraction.