Caesium

Name:Cesium (USA name)
Symbol:Cs
Atomic Mass:132.9054519 g
Atomic Number:55
Density:70.94 g/cm^3
Melting Point:28.44 °C
Boiling Point:671 °C
Group Number:1
Group Name:Alkali Metals
Standard State:solid at room temperature (298 K) (but melts only slightly above this temperature)
Color:silvery gold
Classification:Metallic
Caesium is known as cesium in the USA.The metal is characterized by a spectrum containing two bright lines in the blue (accounting for its name). It is silvery gold, soft, and ductile. It is the most electron-positive and most alkaline element. Cesium, gallium, and mercury are the only three metals that are liquid at or around room temperature. Cesium reacts explosively with cold water, and reacts with ice at temperatures above -116°C. Cesium hydroxide is a strong base and attacks glass.

Isolation

Cesium (cesium in USA) would not normally be made in the laboratory as it is available commercially. All syntheses require an electrolytic step as it is so difficult to add an electron to the poorly electronegative cesium ion Cs⁺.

Cesium is not made by the same method as sodium as might have been expected. This is because the cesium metal, once formed by electrolysis of liquid cesium chloride (CsCl), is too soluble in the molten salt.

cathode: Cs⁺(l) + e^- → Cs (l) anode: Cl^-(l) → ¹/₂Cl₂ (g) + e^-

Instead, it is made by the reaction of metallic sodium with hot molten cesium chloride.

Na + CsCl Cs + NaCl

This is an equilibrium reaction and under these conditions the caesium is highly volatile and removed from the system in a form relatively free from sodium impurities, allowing the reaction to proceed. It can be purified by distillation.