How fast does cesium react with water?

How Caesium Reacts with Water

When it comes to the alkali metals, reactivity increases as you move down the periodic table. Caesium takes this to the absolute extreme, making its interaction with water one of the most violent and dramatic reactions in chemistry.

Unlike less reactive metals like sodium or potassium—which fizz, dart across the surface, and sometimes ignite hydrogen gas—caesium reacts with explosive speed the exact microsecond it touches water. The reaction is so violently instantaneous that it generates an immediate explosion, shattering any standard glass container holding it and leaving virtually no time for hydrogen gas to safely accumulate or ignite gradually.

Because it reacts so aggressively with both moisture and oxygen in the air, caesium cannot be kept out in the open. Instead, chemists must store it securely inside vacuum-sealed borosilicate glass ampoules to completely isolate it from the surrounding environment and prevent catastrophic accidents.