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Chapter 8 - Reactivity trends II - Halogens, image - Coggle Diagram
Chapter 8 - Reactivity trends II - Halogens
Trends in boiling points
At RTP, all halogens exist as diatomic molecules
Boilng points increase down the group due to there being more electrons, stronger london forces which means more energy required to break intermolecular forces
As solids, halogens form lattices with simple molecules structures
Redox reactions
Each halogen has seven outer-shell electrons
Halogen atom is reduced, gaining one electrons form a 1- halide ions
Another spcies loses electrons to halogen atoms an is oxidised
Halogen is the oxidising agents as it has oxidised another species
Halogen halide displacement reactions
Reactivity of halogens decreases down the group
Process
Solution of each halogen is added to aqueous solution of the other halides
If the added halogen is more reactive, a reaction takes place, the halogen displaces the halide ions from the solution and it changes colours
Iodine and bromine look very similar in water, dissolving them in a non-polar solvent like cyclohexane means they are easier to tell apart
Non-polar halogens dissolve more readily in cyclohexane than in water
Colours
Solution in water
Chlorine - pale green
Bromine - orange
Iodine - brown
Solution in cyclohexane
Chlorine - pale green
Bromine - orange
Iodine - violet
Reactivity
Fluorine is a pale yellow gas and reacts with most things
Astatine is extremely rare as it is radioactive and decay rapidly
Trends
Halogens react by gaining electrons
Down the group
Atomic radius increases
Shielding increases (more inner shells)
Less nuclear attraction to capture an electron
Reactivity decreases
Fluorine is the strongest oxidisng agent as it gains electrons more easily
Halogens become weaker oxidisng agents down the group
Disproportionation
Redox reaction where the same elemebt is reduced and oxidised
Chlorine and water
Chlorine is used in water purification
Adding chlorine to water produces chloric and hydrochloric acid
Bacteria is killed by chloric(I) acid and chlorate(I) ions
Chloric acid is a weak bleach
Chlorine and cold, dilute aqueous NaOH
Chlorine isn't very soluble in water
If water contains dissolved sodium hydroxide, much more chlorine dissolved
Resulting solution contains large concentration of chlorate(I) ions from the sodium chlorate(I)
Used as household bleach
Hot concentrated NaOH
Produces Sodium Chlorate(V), sodium chloride and water
Benefits and risk of chlorine
Risks
Extremely toxic
Respiratory irritant in small concentrations, in large concentrations it's fatal
Can react with organic hydrocarbons (methane) to form chlorinated hydrocarbons which are suspected of causing cancer
Benefits
Without it, quality of drinking water would be poor
Diseases like typhoid and cholera would break out
Test for halide ions
Aqueous halide ions react with aquous silver ions to form precipiates of silver halides
Reducing agents
In the displacement reactions between halogen and halide ions, halogen gans electrons and halide ions lost electrons
Halogens are oxidisng agents
Halide ion are reducing agents
Investigation
Reducing ability can be show by a reaction with sulfuric acid (strong oxidising agent)
If there is a reaction, halide ionis are oxidised to form hydrogen
Chloride ions aren't powerful enough to reduce H2SO4
Bromide ions are more powerful an can reduce H2SO4 to SO2
Ioidie ions are even more powerful and reduce the sulfur dioxide formed to sulfur, which is then reduced to H2S
