The Halogens are a group of poisonous non-metals which all have coloured vapours. They are fairly typical non-metals:
- They have low melting points and boiling points
- They are also poor conductors of heat and electricity
The Halogens all look different. At room temperature fluorine is a very reactive, poisonous, pale yellow gas, while chlorine is a reactive, poisonous dense green gas.
It is important to be able to detect chlorine if it is given off. It has a very distinctive smell - you'll recognise it from swimming pools. But it is much safer to hold a piece of damp litmus paper in an unknown gas. If the damp litmus paper is beached, the gas is chlorine.
Bromine is a dense, poisonous dark orange-brown liquid which vapourises eaily - it is volatile. Iodine is a poisonous dark grey crystalline solid which produces violet-coloured vapour when we heat it.
As elements, the Halogens all exist as molecules made up of pairs of atoms, joined together by covalent bonds. (We call this type of molecule a diatomic molecule)
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