Sodium reacting with oxygen in air. It is evident. compared to lithium, that sodium is a softer metal and easier to cut. It is a little more difficult to observe any reaction of air with the newly exposed surface of the sodium. Some change is observed but it is not as easy to see. There is a reaction of oxygen with the sodium. Sodium is stored in heavy petroleum (a hydrocarbon like hexane) liquid to keep it from reacting with oxygen in air, or any water in air.