Transition and Inner Transition Elements — Chemistry STD 12 Science — Question
Maharashtra BoardEnglish MediumSTD 12 ScienceChemistryTransition and Inner Transition Elements3 Marks
Question
Write a note on Lanthanoid contraction. Write two uses of $KM \square O _4$.
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Answer
$1)$ Definition of Lanthanoid Contraction: The Lanthanoid contraction may be defined as gradual $($or small$)$ the decrease in atomic and ionic radii of lanthanoids with the increase in atomic number.
$2)$ In Lanthanides, after Lanthanum $\left({ }_{57} L a\right)$, the electrons are added to anti$-$penultimate shell i.e. $4 f$ orbital.
$3)$ There are $14$ Lanthanoides from ${ }_{58} Ce$ to ${ }_{57} Lu$
$4)$ For each electron, one proton is also added to the nucleus of the atom of the element. Hence from ${ }_{58} Ce$ to ${ }_{71} Lu$ as atomic number increases, nuclear charge increases, therefore nuclear attraction increases.
$5)$ Due to this as atomic number increases, atomic volume or radius decreases as observed with all the elements along the period.
$6)$ But in case of Lanthanoids, this decreases in atomic volume or radius is very slow or comparatively small. This is explained in terms of Lanthanoid contraction
Uses of $KMnO_4:$
$i.$ Used as an antiseptic.
$ii.$ Used for unsaturation tests in the laboratory.
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