[Folypeelarks]

Hi,

I am trying to find information about the chemical properties of alkaline earth metals and I was a little bit confused about the exposure of Calcium to air.
As I understand Magnesium would react with Nitrogen only by burning the metal in higher temperatures and so as Strontium while the oxides are formed in normal conditions \although much more time is needed for Mg\.
But I find different opinions about Calcium, so does the metal reacts with Nitrogen in normal conditions or higher temperature is needed?

[AndersHoveland]

This is an excellent question, and I to would be interested to know the answer.
Calcium certainly can burn in pure nitrogen gas, but whether it slowly reacts at ambient temperatures is uncertain.
I would think it would not, however, because metallic calcium is soluble in liquid anhydrous ammonia. Higher temperatures or a catalyst is required for a reaction. In comparison, the surface of a piece of calcium immediately reacts with water.

[zolarpwr]

Calcium nitride may form in small amounts in dry air, but the oxide will predominate because the greater reactivity of oxygen overcompensates for the higher concentration of nitrogen.

If moisture is present (most likely) the nitride that forms may react further with water to form the hydroxide, limiting the amount of nitride even more.

[Folypeelarks]

Thanks a lot for this answer!

[ajkoer]

My source ("Concise Encyclopedia Chemistry by deGruyter) says something a little different. At normal temperature, Ca rapidly acquires a layer of nitride and oxide, but forming chiefly nitride. At higher temperature both CaO and Ca3N2 are formed.

FYI, when Ca is hot, it reacts with NH3 forming a nitride and a hydride.

6 Ca + 2 NH3 -->   Ca3N2 + 3 CaH2

[enahs]

Someone left some calcium in my glovebox in an open container. The glovebox was obviously 100% nitrogen environment.  The box also happened to be at ~30 C at the time.
By the next day it was all calcium nitride.