Group 7 - Halogens

What is Group 7 made up of?

Fluorine, chlorine, bromine, iodine and astatine

Why do all Group 7 elements have similar chemical properties?

Because they all have 7 electrons in their outer shell

How do halogens exist?

As diatomic molecules (e.g. Cl_2, Br_2, I₂) sharing one pair of electrons in a covalent bond gives both atoms a full outer shell

What happens as you go down Group 7?

The melting points and boiling points of the halogens increase

What happens when the halogens are at room temperature?

• Chlorine (Cl₂) - is a fairly reactive, poisonous, green gas

• Bromine (Br₂) - is a poisonous, red-brown liquid which gives off an orange vapour

• Iodine (I₂) - is a dark grey crystalline solid which gives off a purple vapour when heated

How can you test to see if a gas is chlorine?

By holding a piece of damp blue litmus paper over it - Chlorine will bleach the litmus paper, turning it white, it may also turn red for a moment first (this is because a solution of chlorine is acidic)

What is the trend for reactivity as you down Group 7?

Reactivity decreases

Why does the reactivity go down as you go down Group 7?

A halogen atom only needs to gain one electron to form a 1- ion with a stable electronic structure - the easier it is for a halogen atom to attract and electron, the more reactive it will be (it gets harder to attract the extra electron to fill the outer shell when it’s further away from the nucleus

What do halogens react with hydrogen to form?

Hydrogen halides

What are the properties of hydrogen halides?

They’re soluble, and they can dissolve in water to form acidic solutions

Why do all halogens have similar reactions?

Because they have the same number of electrons in their outer shell - therefore you can you use the reactions of chlorine, bromine and iodine to predict how fluorine and astatine will react