Halogens
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What are the melting and boiling points like?
Halogens have low melting and boiling points, which increase as you go down the table.
What states are they?
Fluoride and chlorine are gases, bromine is a liquid, iodine and astatine are solids.
Describe the reactivity
Reactivity decreases as you go down the group. Fluorine is very reactive. This is shown by the displacements tests.
Describe and explain the displacement reaction
You add one of the halogens to a halogen salt. The less reactive halogen will be ‘kicked out’ by the other one. E.g. Chlorine + sodium bromide => bromine + sodium chloride This is a redox reaction. The bromine loses electrons and the chlorine gains electrons
What are the colours of the halogens?
They get darker as you go down the group. Fluorine pale yellow Chlorine yellow-green Bromine red brown. Bromine water oranges Iodine grey, turn to a dark purple vapour when warmed
What’s the difference between hydrogen chloride gas and hydrochloride acid?
• HCl is the gas • when in gas, the H atoms can’t disaccociate from the molecule ∴ no H+ atoms, so doesn’t behave like acid • in aqueos form, H atoms can disassociate from molecules ∴ H+ atoms present ∴ behave like an acid
Why’s hydrogen chloride acidic in water but not methylbenzene?
• hydrogen chloride is a polar molecule, and they can only disassociate in other polar molecules • water is polar, methylbenzene isn’t • when HCl is dissolved in H₂O you get H+ ions = acidic
What are the uses of some of the halogens?
Cl- sterilising water Br- pesticides and plastics I- sterilising wounds