The Halogens Flashcards
What do all halogens exist as
Diatomic molecules held by a single covalent bond
Each atom has 3 lone pairs
Describe the trend boiling points down the halogen group
It increases
Due to the London force strength increasing as the number of electrons in the molecule increase ( which occurs as you go down the group)
How does the atomic radius change down the group
Increases
How does the 1st ionisation energy change down the group
Decreases
How does the electron infinity and bond dissociation energy change down the group
Decreases
However fluorine is lower then chlorine as due to its size the lone pairs repel eachother
What agents are halides
Oxidising agents
How does the ionic radius compare to the atomic radius
It is larger due to no change in nuclear charge and an extra electron so a weaker attraction is felt
Halogens + silver nitrate
Cl=white
Br=cream
I= yellow
Halogens + silver nitrate + dilute ammonia
Cl= ppt redissolves
Br= no change
I= no change
Halogens + silver nitrate + conc ammonia
Br= ppt redissolves
I= no change
Ionic equation for halogens + silver nitrate
Ag+ + X- —-> AgX
What is the trend in strength of oxidising agents
Decrease due to atoms become larger, radius increases, more shielding = less attraction for electron being gained
What does cl2 displace
Bromine and iodine
What does br2 displace
Iodine
What dies I2 displace
None
What do halide ions act as
Reducing agents as they are oxidised to form halogens
They increase in strength as reducing agent
What can chlorine do in water
Kill bacteria
What is the equation for chlorine and water
What is this called
Where does the equilibrium lie
Cl2 (aq) + H2O ——>(reversible) HCl (aq) + HOCl (aq)
Disproportionation
To the left hand side
HOCl is chloric acid
Is chloric acid strong or weak and how does it dissociate
What is formed
Weak
HOCl (reversible arrow ) H+ + ClO-
Chlorate ions are oxidising agents that kill bacteria
Benefits to using chlorine to treat water
- kills microorganisms
- some chlorine will remain dissolved in the water which prevents re infection
- prevents algae removes bad tastes and can remove discolouration
Disadvantages of using chlorine to treat water
- chlorine gas toxic and corrosive. Harmful to respiratory system
- concerns that chlorine can react with organic compounds (pollution) in the water to form chlorinated organic compounds that may be carcinogenic
What are the alternatives instead of using chlorine to treat water
Ozone (O3)
Ultraviolet light
Details on ozone in treating water
Strong oxidising agent so good at killing microorganisms
Toxic, expensive, not long lasting
Details on UV in treating water
Destroys microorganisms by damaging DNA preventing reproduction
Ineffective in cloudy water
Not effective against future contamination
