Periodic Table
Group 1: Alkali metals
Group 0: Noble Gases
Group 7: Halogens
Transition metals
The Table

Organic Chem.

The Halogens

the halogens


The halogens are in group 7, and are therefore non-metals. Above is the group presented horizontally (vertical in periodic table) and below is a table of their colours and state at room temperature (25°C).

Fluorinepale yellowgas
Chlorineyellow - greengas
Iodinedark greysolid

Note Astatine is a radioactive and very rare element, in fact it is thought to be the rarest naturally occuring element on earth.


Halogens will react with metals to form salts. For example, if chlorine gas is passed over a heated iron wire, you will see a brown solid upon cooling.

iron + chlorine ® iron (III) chloride
2Fe(s) + 3Cl2 (g) ® 2FeCl2 (s)

The most reactive halogen is fluorine, and they become less reactive as you go down. Due to this, a more reactive halogen will displace a less reactive one. For example, when chlorine gas is bubbled though potassium bromide solution...

2KBr(aq) + Cl2 (g) ® 2KCl (aq) + Br2 (aq)


Fluorides are used in toothpaste and water supply because they help to keep your teeth clean.

Chlorine is used in water purification because it kills bacteria.

Iodine is used as an antispetic and you often see it smeared on patients at hospitals.