A Visual Encyclopedia of the Periodic Table

180

The Halogen Group

This glass sphere

traps pure chlorine

so as to prevent any

reactions with air.

Forms

Chlorine

Cl

17

17 17 18

State: Gas

Discovery: 1774

Chlorine is named after the Greek word

chlóros, which means “pale green”, a reference

to the colour of this gaseous element. Chlorine

is a highly reactive gas that forms a number of

compounds, and does not exist pure in nature.

The most common chlorine compound is sodium

chloride, found in nature as the mineral halite.

Chlorine compounds are important for the body

and are used by muscles and nerves. They are also

present in sweat. As it is poisonous in its pure form,

chlorine gas was used as a weapon during World

War I: soldiers had to wear masks for protection

This orange colour is

due to the presence of

the mineral hematite.

The intense red

colour is due

to impurities.

The skin of this tree frog

contains a chlorine compound.

Cube-shaped cr ystals

Halite

Carnallite

Re

d-e

ye

d^ t

ree

fro

g

a (^) g
las
s (^) s
ph
er
e
Pure
chlorine
is heavier
than air.
Pu
re
ch
lor
in
e (^) i
n
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