Chemistry class 12th Variation_Atomic_Ionic_Sizes_Transition_Metals

Variation in Atomic and Ionic Sizes of Transition Metals


1. Atomic Radii Trends in Transition Metals


Across a Period (Left to Right in a Series):
- Atomic radii decrease slightly due to increased nuclear charge.
- Shielding effect of d-electrons partially counteracts the contraction.
- After the middle of the series (around Fe, Co, Ni), the radii remain almost constant due to
electron-electron repulsion.


Down a Group (From One Series to Another):
- Atomic size increases from 3d to 4d, but 4d and 5d sizes are almost identical due to lanthanide
contraction.


2. Ionic Radii Trends in Transition Metals


For a Given Charge (Across a Series):
- Ionic radii decrease across the period due to increasing nuclear charge.
- Example: Fe2+ > Co2+ > Ni2+.


For a Given Element (Different Oxidation States):
- Higher oxidation states have smaller ionic radii due to stronger nuclear attraction.
- Example: Fe3+ is smaller than Fe2+.


Key Factors Influencing These Trends:
1. Nuclear Charge (Zeff) - More protons attract electrons closer.
2. Shielding Effect - d-electrons are less effective at shielding, leading to stronger nuclear attraction.
3. Electron-Electron Repulsions - Increase repulsions, slowing down contraction.
4. Lanthanide Contraction - 5d elements are almost the same size as 4d due to poor shielding of 4f
orbitals.