Sodium monoxide, Na₂O

The monoxide is produced by combustion of sodium in dry air, the peroxide being formed simultaneously; or by heating the hydroxide or peroxide with sodium -

2NaOH+2Na=2Na₂O+H₂

Sodium monoxide is a white substance when cold, pale-yellow when hot, and melts at bright redness. It is very hygroscopic, combining with water to form the hydroxide, the heat evolved being 56.5 Cal. For the density Beketoff gives 2.314, and Rengade 2.27. The heat of formation from the elements is 100.7 Cal. Above 400° C. it yields equimolecular proportions of sodium and sodium peroxide. It is converted by hydrogen into an equimolecular mixture of sodium hydroxide and hydride, and it also combines with fluorine, chlorine, and iodine.

The so-called "sodium suboxide," obtained by combustion of sodium in a limited supply of oxygen, seems to be either a mixture or solid solution of sodium and sodium monoxide.