How to Enlighten the Preference for a Particular Oxidation State of an Element in a Salt – Part 1

Redox, reduction–oxidation or oxidation–reduction is a type of chemical reaction in which the oxidation states (OSs) of the reactants change.


The shielding effect aka screening effect, atomic shielding, or electron shielding describes the attraction between an electron and the nucleus in any atom with more than one electron (where the core electrons tend to shield the valence electrons against the nuclear attraction), and is a reduction in the effective nuclear charge on the electron cloud.

Question:

Why PbCl2 is more stable than PbCl4 when SnCl2 is less stable than SnCl4?

Solution:



Click/tap to enlarge the image

EC = Electron configuration

Similarly, Tl+ is more stable (inert pair effect) than Tl3+ when In+ is less stable than In3+. ECs of Tl & In are [Xe] 4f145d106s26p1 & [Kr] 4d105s25p1 respectively.

The lanthanoid/lanthanide and actinoid/actinide contractions are the steady, greater-than-expected decrease in atomic and ionic radii of the lanthanoid elements La-Lu (atomic numbers 57-71) and actinoid elements Ac-Lr (atomic numbers 89-103) respectively from left to right, and caused by the poor shielding effect of the diffused 4f & 5f electrons respectively as nuclear charge increases, pulling the electron cloud closer. The contraction results in unexpected high density and similar properties making them difficult to separate.

Actinoid contraction is more pronounced than lanthanoid contraction as the 5f electrons in actinoids provide even poorer shielding (more diffused) compared to the 4f electrons in lanthanoids. The contraction is typically steady for trivalent ions (M3+) across the series.

Chromium (Cr) to Copper (Cu), the atomic radii are nearly constant or change very slowly, as the increased shielding effect of the 3d electrons almost offsets the increasing nuclear charge.

Sensible shielding ❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com❗

NOTE: Post updated since published

References:

(1)    Wikipedia Contributors. Redox. Wikipedia. https://en.wikipedia.org/wiki/Redox.

‌‌(2)    Ncert. Chemistry : Textbook for Class XII - Part.I; National Council Of Educational Research And Training: New Delhi.

(3)    Brown, C.; Ford, M. Higher Level Chemistry, 2nd ed.; Pearson Education: Harlow, Essex, 2014.

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