The iron is found to have four unpaired electrons while vanadium has 3 of them. we say the binding energy is directly proportional to number of unpaired electrons and hence number of metallic bonds in the structure. By this logic, iron should have high melting point than vanadium but no. Iron has a m.p of 1535 degree celsius while vanadium has 1917.

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    $\begingroup$ Atom-level (chemistry) concepts don’t translate well to crystal (solid state physics) bonding. $\endgroup$
    – Jon Custer
    Oct 21 '20 at 16:09

@Jon Custer makes a good point in his comment so lets look beyond the electronic shell configuration of V and Fe to help understand the different in melting points.

Consider the following:

Pauling’s Electronegativity Fe > V 1.8 vs 1.6

Vander walls radius Fe < V 0.126 nm vs 0.134 nm

And consistent with Fe having a higher electronegativity the first ionization energy of Fe [761 kJ per mol] is greater than that of V [ 649.1 kJ per mol]

Given that we think of melting as the breaking of lattice forces holding atoms together, Fe being a smaller and more electronegative atom [vs V] is consistent with the relative melting points of these two elements.

Ref: https://www.lenntech.com/periodic/elements/fe.htm



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