New Year's Countdown Day 23: Have a "V"ery Nice Holiday!
Chemistry
Level
2
Which of the following compounds has the lowest melting point?
Bonus: Why?
This problem is part of the set New Year's Countdown 2017 .
Vanadium(V) oxide
They all have similar melting points
Vanadium(IV) oxide
Vanadium(II) oxide
Vanadium(III) oxide
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1 solution
If you searched this up online, you would have found that vanadium(V) oxide has a much lower melting point than the other vanadium oxides: 690°C compared to 1700+°C. I cannot find an official explanation for why this is, but here's my attempt:
All four vanadium oxides form crystal lattices. Both vanadium(II) oxide and vanadium(IV) oxide have linear molecular structures, so relatively speaking, their lattices are very strong due to the increased possibilities for intermolecular attractions for both molecules. Vanadium(III) oxide has a zig-zag molecular structure, making it have a dipole moment. Dipole-dipole attractions require lots of energy to break, so vanadium(III) oxide also has a relatively high melting point.
However, vanadium(V) oxide has an "awkward" molecular structure, giving it limited ability to form intermolecular attractions:
Thus, the energy required to melt vanadium(V) oxide should be lower than the other vanadium oxides, since the IMFs are not as strong.
Again, I can't seem to find a source to back this up, so let me know if any of the above was wrong or if you could find a better official explanation.