Halogens

Where are the halogens on the periodic table?

group 7

What are some examples of halogens? Give colours & physical states

chlorine → yellow / green gas

bromine → red-brown liquid

iodine → purple solid

What are the trends in Group 7?

- halogens go from gases → liquids → solids down the group

- melting & boiling points increase down the group

- reactivity decreases down the group

How can group 7 trends be used to predict the properties of other halogens?

- you can predict than any element above chlorine will be a gas & have a lower melting / boiling point

- you can predict that any element below iodine will be a solid & have a higher melting / boiling point

What is a displacement reaction?

when a more reactive element displaces a less reactive element from its compound

How do displacement reactions involving halogens & halides provide evidence for group 7 trends?

- a more reactive halogen can displace a less reactive halogen in an aqueous solution of its salt (e.g. chlorine will displace bromine when bubbled through a solution of potassium bromide → Cl₂ + 2KBr → 2KCl + Br₂)

- this supports the group 7 trends as it shows how reactivity decreases down the group

Why does reactivity decrease down group 7?

- because halogens react by gaining 1 electron in their outer shell & as the group goes down, the number of screening electron shells increases which means that the outer shell is further away from the nucleus

- this makes it harder for the halogen to gain 1 electron because the electrostatic force of attraction between the positive nucleus & negative electron is weaker