Sciencemadness Discussion Board

Why does Radium form a nitride and not oxide?

Whathappensif - 10-7-2020 at 11:15

Curious behavior. Anyone know any other elements that burn to preferentially form a nitride instead of an oxide?

Why does this happen?

https://en.wikipedia.org/wiki/Radium
Quote:

Radium is a chemical element with the symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is silvery-white, but it readily reacts with nitrogen (rather than oxygen) on exposure to air, forming a black surface layer of radium nitride (Ra3N2).

Mateo_swe - 11-7-2020 at 07:07

Maybe due to the alpha radiation radium emits.
It would be interesting to know why that happens.
Any nuclear hobbyists here?

RedDwarf - 11-7-2020 at 10:22

I don't think it to do with the radioactivity as all the alkaline earth metals from magnesium onwards produce a mixture of oxide and nitride when burnt in air, and I think the propensity to produce nitride increases as you go down the group. As to why, I've still no idea.

phlogiston - 11-7-2020 at 14:17

It is discussed on this page.

They attribute it to the high lattice energy of the nitrides, due to the highy charged ions involved (2+ and 3-).

BTW, I suspect aluminium also forms nitrides to a lesser extent upon heating in air, as I've noticed a strong ammonia smell when casting aluminium objects and quenching them in water.

I doubt there is a very significant difference in the rate at which Ba and Ra form nitrides or oxides. If there was, surely it would have been exploited to separate Ra from Ba.

[Edited on 11-7-2020 by phlogiston]