The oxide Na2O is strongly basic, like Li2O. It forms ionic crystals of two Na+ to each O2- ion, with the same structure as Li2O.

Because Na2O is very hygroscopic (meaning that it will absorb water from the atmosphere), it is a good drying agent.

It dissolves in water to produce a strongly basic solution of Na+ and OH­ ions, which upon drying yields crystalline sodium hydroxide (see right):

Sodium hydroxide, commonly known as caustic soda or lye, is the most common laboratory and industrial source of hydroxide ions.