MadSci Network: Chemistry |
I am not an inorganic chemist, but the question is intriguing. My guess would be that Group VIB (IUPAC Group 6) has six valence electrons -- but a half-filled d subshell shell is especially stable. This means that the outer s subshell tends to have just one electron, possibly encouraging metallic bonding to the point that the bond becomes much stronger and the metals have rather higher melting points. From this argument one would expect Group VIB metals to also be harder, and in fact my CRC handbook says that chromium has a Moh's hardness of 9 (where diamond is 10); manganese (Group VIIB, same row) has a hardness of 5. Unfortunately I was unable to find hardnesses for other metals in the "neighborhood." You may want to forward this to a solid-state physicist for comment. Dan Berger
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