group 7 (halogens)

what colour and physical state is chlorine?

pale green, gas

what colour and physical state is bromine?

brown, liquid

what colour and physical state is iodine?

purple-black, solid

what are the trends in group 7?

as you go down the group, melting point increases, boiling point increases, colour becomes darker and reactivity decreases

what is a displacement reaction?

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

e.g. chlorine + potassium bromide → bromine + potassium chloride (chlorine displaces bromine as chlorine is more reactive)

iodine + potassium bromide → iodine + potassium bromide (no change as iodine is less reactive than bromide)

why do halogens become less reactive down the group?

halogens react by gaining one electron to form a 1- ion

a chlorine atoms has less shells than a bromine atom, so its outer shell is closer to the nucleus. This means the added electron will be more strongly attracted to the nucleus, so it has a stronger tendency to form a 1- ion than bromine

inner electrons also shield the outer electrons from the attraction of the nucleus, so since bromine has more electron shells the outer shell will have more shielding, making it harder to gain an electron