D-block Contraction – Everything You Need to Know About

D-block Contraction – Everything You Need to Know About

The d-block Contraction is also known as the Scandide Contraction.

The effect of the D block contraction occurs on the period 4 elements due to the full d orbitals. This contraction thing affects the elements Gallium (Ga), Germanium (Ge), Arsenic (As), Selenium (Se), Bromine (Br), and Krypton (Kr) mainly.

Electronic configurations of all these elements in question have fully filled d orbitals i.e. d10.

In this blog post, we will be taking a quick look at everything you need to know about the D-block Contraction.

Here we go then…

D-block Contraction
The atomic radius of elements of the groups 2, 13 and 14. It shows the “d block contraction”, especially for Ga and Ge

What is D Block Contraction

In order to better understand the d block contraction, let’s compare some of the properties of the elements of group 13 in order to highlight the effect on the Gallium.

Element Sum 1st – 3rd
I.Ps kJ/mol
M3+ radius (pm)
Boron (B) 6887.4
Aluminium (Al) 5139 53.5
Gallium (Ga) 5521.1 62
Indium (In) 5083 80
Thallium (Tl) 5438.4 88.5

Here, it can be seen that the Gallium is anomalous and the most obvious effect is that the sum of the first 3 ionization potentials of Gallium (Ga) is way higher than that of Aluminium (Al) but it should have been lower as per the trend. Also, the radius of the Ga3+ ion is smaller than the expectations.

Let’s take a look at another table containing the same details of the group 3 elements which are Boron (B), Aluminium (Al), Scandium (Sc), Yttrium (Y), and Lanthanum (La).

Element Sum 1st – 3rd
I.Ps kJ/mol
M3+ radius (pm)
Boron (B) 6887.4
Aluminium (Al) 5139 53.5
Scandium (Sc) 4256.7 74.5
Yttrium (Y) 3760 90
Lanthanum (La) 3455.4 103.2

So, what did you observe?

The sums of the first 3 ionization potentials of the group 3 elements is a way more smooth than that of the group 13 elements.

Note: In the heavier members of the group like Indium and Thallium, you might also need to consider some other effects like Inert Pair Effect while interpreting the Ionization Potentials.

What Causes the D Block Contraction

So, the main reason of the d-block contraction is the poor shielding of the nuclear charge by the electrons in the d orbitals. These cause a considerable increase in the Ionization Potentials because the outer valence electrons are more attracted by the nucleus.

This d-block contraction may be compared to the Lanthanide Contraction which is also caused by the inadequate shielding of the nuclear charge by the electrons occupying f orbitals.

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Wrapping it up

So, that’s it.

There is not much to explain in this d block contraction theory.

But, if you have got any related query then be sure to let me know in the comments below.

Also, share this informative piece of article with the people who you think might be interested in reading it.

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