Cesium (Australian English: caesium) (atomic symbol Cs) is element 55 on the periodic table. It is in the alkali metals family and is therefore extremely reactive with water, similarly to sodium and potassium but to a greater extent. It is lustrous in appearance, with a slight yellow/golden tint, and melts at 28˚C (82˚F) meaning that it is almost liquid at room temperature.
590px-Cesium ampoule in acrylic cube