Lanthanide Contraction is one of the interesting exceptions to study in the Chemistry subject.
Sometimes, it is also known as the Lanthanoid Contraction.
It applies to the elements in the Lanthanide Series of the Periodic Table. Lanthanide series ranges from atomic number 57 to atomic number 71.
In this blog post, Like the d-block contraction, I will be talking also about the Lanthanide or Lanthanoid Contraction in detail.
So, here we go…
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What is Lanthanide Contraction?
Sudden decrease of the ionic radii of the elements of the periodic table in the Lanthanide Series is called the lanthanide contraction.
According to Wikipedia,
The lanthanide contraction is the greater-than-expected decrease in ionic radii of the elements in the lanthanide series from atomic number 57, lanthanum, to 71, lutetium, which results in smaller than otherwise expected ionic radii for the subsequent elements starting with 72, hafnium.
So, in this contraction, with the increase in the atomic number, size of atoms and ions from Lanthanum (atomic no. 57) through Lutetium (atomic no. 71) decreases more than the expected value.
This contraction was discovered by the Norwegian geochemist named Victor Goldschmidt.
How many Elements of the Periodic Table does Lanthanide Contraction Apply to?
Well, as mentioned above, it applies to the elements of the lanthanide series only. And, there are a total of 14 elements in the series.
All the 14 elements of the series are:
|Atomic Number||Element||Element (Full Name)||Ln3+ radius (pm)
What Causes Lanthanide Contraction
6s electrons are drawn towards the nucleus due to the poor shielding of nuclear charges by 4f electrons. The movement of the 6s electrons towards nucleus results in the smaller atomic radius.
Shielding effect is also known as the atomic shielding or electron shielding which explains the attraction between an electron and the nucleus inside a multi-electron atom.
Effects on the Lanthanides
Due to this lanthanoid or lanthanide contraction, outer shell electrons are more attracted towards the nucleus across the lanthanides which results in considerably smaller ionic radii.
This contraction also affects the post-lanthanide series elements of the periodic table.
Effects on the Post-lanthanides
Lanthanide contraction doesn’t only affect the lanthanides (from atomic number 57 to 71), but also the elements after.
Let’s compare the atomic radius and ionic radius of Zirconium and Hafnium. Zirconium (atomic number 40) lies prior to the lanthanides and Hafnium (atomic number 72) lies just after the lanthanides.
Atomic Radius of Zirconium is 159 pm & Hafnium is 156 pm
Ionic Radius of Zr4+ is 79 pm & Hf4+ is 78 pm
You can see the decrease in the atomic as well as the ionic radii of these two pre and post lanthanides.
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So, that’s it and I hope this explains everything.
Lanthanide Contraction is considered to be one of the most interesting topics and also very important for Chemistry students.
If you have any related query or doubts then let me know in the comments right now.
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