Name: caesium
Symbol: Cs
Atomic number: 55
Atomic weight: 132.90545 (2)
Group in periodic table: 1
Group name: Alkaline metal
Period in periodic table: 6
Block in periodic table: s-block
CAS registry ID: 7440-46-2
Caesium is known as cesium in the USA.
The metal is characterised by a spectrum containing two bright lines in the blue (accounting for its name). It is silvery white, soft, and ductile. It is the most electropositive and most alkaline element. Caesium, gallium, and mercury are the only three metals that are liquid at or around room temperature. Caesium reacts explosively with cold water, and reacts with ice at temperatures above -116°C. Caesium hydroxide is a strong base and attacks glass.