8.2 The Halogens
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What is the most reactive non metallic group?
Group 17
How are the group 17 elements found in nature?
Stable halide ions dissolved in sea water Combined with Sodium and Potassium as solid deposits
How do halogens exist at RTP?
Diatomic molecules
Appearance of F2
Pale yellow gas
Appearance of Cl2
Pale green gas
Appearance of Br2
Red brown liquid
Appearance of I2
Shiny grey black solid
Appearance of At2
Never been seen
What happens to boiling point going down group 17?
Boiling point increases
Why does boiling point increase going down group 17?
More electrons Stronger London forces More energy required to break the intermolecular forces Boiling point increases
Outer shell electrons in halogens?
7 electrons 2 in the s sub shell 5 in the p sub shell
Most common reaction for halogens
Redox reactions
What happens to halogens during redox reactions?
Each Halogen atom is reduced, gaining an electron, forming a 1- ion Acts as an oxidising agent, oxidising another species
What happens to reactivity of halogens going down the group?
Reactivity decreases
What happens during halogen-halide displacement reactions?
A more reactive halogen displaces a less reactive halogen in a compound
Experiment to show reactivity of halogens
Solution of each halogen is added to aqueous solutions of other halides If halogen added is more reactive than the halide, displacement reaction takes place Solution changes colour
How can you tell apart bromine and iodine in water?
Organic non polar solvent like cyclohexane can be added and mixture is shaken Non polar halogens dissolve more readily in cyclohexane than water Here, the colours are easier to tell apart Bromine - orange Iodine - purple
Reactivity of Fluorine
Reacts with almost any substance it comes into contact with
Reactivity of Astatine
Radioactive - decays rapidly Element has never been seen, but predicted to be most reactive halogen
Explain trend in reactivity going down group 7
Atomic radius increases More inner shells so electron shielding is increased Less nuclear attraction to attract an electron from another species Reactivity decreases going down the group
Which halogen is the strongest oxidising agent?
Fluorine
What is a disproportionation reaction?
A redox reaction where the same element is both oxidised and reduced
Examples of disproportionation reactions
Chlorine and water Chlorine and cold, dilute Sodium Hydroxide
Why is chlorine used in water treatment?
Reducing prevalence of waterborne diseases by killing harmful bacteria