Why are there peaks in electronegativities in d-block elements?

Looking at the Pauling electronegativities in the Periodic Table (below, from [ChemWiki](http://chemwiki.ucdavis.edu/Physical_Chemistry/Physical_Properties_of_Matter/Atomic_and_Molecular_Properties/Electronegativity/Allred-Rochow_Electronegativity)):


![enter image description here](https://i.stack.imgur.com/80wJk.gif)


Asides from the overall trend of increasing electronegativity across and up the Periodic Table (towards fluorine), there seems to be a minor peak in the first 3 periods of the $d$-block elements, this peak becomes more pronounced as you go down the $d$-block, with the most noticable peaks in Periods 5 and 6 - seemingly the reverse of the overall trend. This is shown in the graph below ([Image source)](http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s11-the-periodic-table-and-periodi.html):


![enter image description here](https://i.stack.imgur.com/xitIQ.jpg)


In the ChemWiki page, there is also a reference to the Allred-Rochow Electronegativity Scale, which also has peaks occurring most prominently in Periods 4 and 6:


![enter image description here](https://i.stack.imgur.com/nHwui.png)


[Image source](https://de.wikipedia.org/wiki/Elektronegativit%C3%A4t#Allred-Rochow-Skala)


The Wikipedia page [Electronegativity](https://en.wikipedia.org/wiki/Electronegativity#Methods_of_calculation) details several methods of calculation, which brings into question how well-defined the electronegativity values are; however, there still seems to be the peaks occurring, particularly in Periods 5 and 6, and to a lesser extent in Period 4.


**What is the reason for these electrongativity peaks in the $d$-block?**




You should know that closeness to filling a shell and atomic size are the reasons for the overall electronegativity trend. This also applies to the subshells, how close is an element to filling, or half-filling, a subshell? How large is the atom?


The atomic size trend for the d subshell is opposite to that of the overall trend. In period 4 the 3d subshell is deep in the core orbitals and the electron density is high, whereas in the lower periods the d orbital is more diffuse and can more easily accommodate more electrons, leading to a better energy payoff for completing the subshell. For the elements that take s electrons to fill the d subshell, this energy payoff is even greater from then filling the s subshell as they are very diffuse.


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The peaks in electronegativity for elements may be named as groups as next:


V Cr Mn has a peak and then Mn drops down. Iron is the key as shown next.
Zr Nb Mo has a peak and then a a plateau. Zirconium is the key as shown next.
My research is displayed : 
Periodic Table of Elements : Shape of Each Nucleus affecting electronegativity


[![enter image description here](https://i.stack.imgur.com/BltJB.jpg)](https://i.stack.imgur.com/BltJB.jpg)
<http://pyramidalcube.blogspot.com/2017/08/periodic-table-of-shapes-of-nuclei.html>
The shape of the nucleus affects the properties of the element. Notice how
Manganese is the last in a series from the carbon core cube-2, then iron starts the cube-3 shape. That transition across the Table causes the abrupt change in electronegativity.
Alan Folmsbee


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