Melting and boiling point of transition-metals, primarily for the groups of Cr and Mn [duplicate]








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[Melting and boiling points of transition elements](/questions/4766/melting-and-boiling-points-of-transition-elements)

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The NCERT Chemistry book for Grade 12 writes



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> The high melting points of these metals are attributed to the involvement of greater number of electrons from $(n-1)d$ in addition to the ns electrons in the interatomic metallic bonding. In any row the melting points of these metals rise to a maximum at $ d^5$ except for anomalous values of Mn and Tc and fall regularly as the atomic number increases.
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However, it mentions no such reason as to why this exceptional/anomalous behaviour is observed. My initial thoughts towards approaching this issue were considering the electronic configurations that group members of Mn have an exceptionally stable half-filled configuration, but a similar half-filled configuration exists with group members of Cr as well. Secondly, I thought it could be due to the structures, the NCERT book also mentions Zn/Cd/Hg/Mn having certain exceptional behaviour when it comes to their structures with respect to the other members of the d-Block, but it doesn't mention the same for Tc which too shows a steady dip in it's melting point.


What could be the possible reason for such anomalous behaviour if not the electronic configuration or the solid structure? Here's the [graph](https://files.askiitians.com/cdn1/images/2014515-121755477-7955-untitled.png) for the melting points for d-Block elements.




One of the factors affecting the melting point of transition metals is the number of **unpaired** electrons in $(n-1)d$ and in $ns$. These unpaired electrons take part in metallic bonding and the more there are, the more bonds and hence greater is the melting point. As we move from left to right in the 3d,4d, and 5d series, the number of unpaired electrons first increases (till $(n-1)d^{5}$) and then decreases as pairing starts.


Manganese shows an exceptionally lower melting point as due to the exceptionally stable half filled configuration, the electrons are not delocalised to a large extent. This occurs in manganese and not in chromium due to the fully filled $4s^{2}$ subshell in manganese, in which pairing has occurred.


This is also the reason why technetium shows a dip in its melting point in the 4d series as it has a $4d^{5}$ $5s^{2}$ configuration.


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