A Visual Encyclopedia of the Periodic Table

34

Alkali Metals

Caesium

Cs

55

Forms Uses

As the most reactive metal on Earth, caesium

explodes into flames if in contact with air or

water. Therefore, pure caesium, is stored in a

sealed glass tube from which all the air has been

sucked out. This element is rare, and most of it

is extracted from the mineral pollucite. Its name

means “sky blue” and refers to the colour of

caesium’s flame when burning. Caesium is used

in atomic clocks, which measure time down

to a billionth of a second. These clocks are so

accurate that they would gain or lose no more

than one second every 300 years.

55 55 78

State: Solid

Discovery: 1860

Caesium was discovered in 1860 by

German scientists Robert Bunsen and

Gustav Kirchhoff. They burned a sample

of mineral water on a burner, which split

the flame’s light into individual colours.

One of them was a distinctive light blue,

which came from caesium.

Gustav Kirchhoff (left) and

Robert Bunsen (right)

Atomic clock

Drilling fluid

The cr ystals of

this mineral are

used in jewellery.

Shiny, silver-gold metal

Sealed

glass tube

High-density caesium

compounds in this fluid

stop toxic gases rising

to the surface.

This highly accurate clock is

also called a caesium clock.

KIRCHHOFF AND BUNSEN

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