Sodium
Sodium is a light-weight, silver-colored metal. Sodium is soft, and because of that, someone could easily cut it with a knife. When someone cuts it, the exposed part will become white over time. It reacts with air to form sodium hydroxide and sodium carbonate. Sodium is a little less dense than water; when someone puts it in water, it floats and reacts instantly, producing hydrogen and sodium hydroxide. This reaction has a lot of heat, usually causing the hydrogen to light on fire. When this happens, sodium melts because of its low melting point. Sodium is highly reactive because it has one valence electron, which is easily removed.