"It began to skate across the surface"

The alkali metals are a group of chemical elements with similar properties: shiny, silvery metals which are soft and highly reactive. Lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs) and francium (Fr) all react violently when introduced to water, producing large amounts of hydrogen gas – lithium has the weakest and francium the strongest reaction. A favourite illustrative experiment of chemistry teachers, only the first three (lithium, sodium and potassium) can be safely demonstrated and even then only using very small amounts; the other elements cause extremely violent and dangerous explosions when introduced to water. The video below shows a small square of potassium introduced to water.