Why can sodium float on water?

Sodium floats on water because it has a lower specific gravity than water. With a specific gravity of approximately 0.971 at 20 °C, sodium is less dense than liquid water, which allows it to remain on the surface.1

It is important to note that while sodium floats, it is highly reactive when it comes into contact with water. This interaction is a violent, exothermic oxidation-reduction reaction that produces sodium hydroxide and releases hydrogen gas. Because this reaction generates heat and flammable hydrogen gas, it can be hazardous.234