The halogens Flashcards
What is Group 7?
The halogens - the most reactive non-metal group
How do the Halogens exist at room temperature and pressue?
As diatomic molecules, X2
What do the halogens form in their solid state?
Lattices with simple molecular structures
What is the trend in boiling point as you go down the halogen group?
- More electrons
- Stronger London forces
- More energy required to break the intermolecular forces
- Boiling point increases
What type of agent is a halogen?
Oxidising agent. It is reduced, and has oxidised another species
Cl2 + 2e- -> 2Cl-
What is the trend in reactivity down the halogens?
It decreases
What do halogen-halide displacement reactions show?
How the reactivity decreases down the halogen group
How are halogen-halide displacement reactions carried out?
A solution of each halogen is added to aqueous solutions of the other 2 halides. If the halogen added is more reactive than the halide present:
- a reaction takes place, the halogen displacing the halide from the solution
- the solution changes colour
Why is cyclohexane used in halogen-halide displacement?
Solutions of iodine and bromine in water can appear similar orange-brown colours, depending on concentration. To tell them apart, an organic non-polar solvent such as cyclohexane can be added and shaken with the mixture. The non-polar halogens dissolve more readily in cyclohexane than in water. In cyclohexane their colours are much easier to tell apart
Whats the colour of Cl2 in water?
Pale green
Whats the colour of Br2 in water?
Orange
Whats the colour of I2 in water?
Brown
Whats the colour of Cl2 in cyclohexane?
Pale green
Whats the colour of Br2 in cyclohexane?
Orange
Whats the colour of I2 in cyclohexane?
Violet
Whats the reaction between Cl - and Br2?
No reaction
Whats the reaction between Cl - and I2?
No reaction
Whats the reaction between Br - and Cl2?
Cl2 (aq) + 2 Br - (aq) -> 2Cl - (aq) + Br2 (aq)
Orange colour from Br2 formation
Whats the reaction between I- and Cl2?
Cl2 (aq) + 2I - (aq) -> 2 Cl- (aq) + I2 (aq)
Violet colour from I2 formation
Whats the reaction between I- and Br2?
Br2 (aq) + 2I- (aq) -> 2Br- (aq) + I2 (aq)
Whats the reaction between Br- and I2?
No reaction
What do the results of the halogen-halide displacements show?
- Chlorine has clearly reacted with both Br - and I -
- Bromine has reacted with I - only
- Iodine has not reacted at all
In the reaction of chlorine with bromide ions, what is reduced and what is oxidised?
Chlorine is reduced
Bromine is oxidised
What is fluorine?
A pale yellow gas, reacting with almost any substance that it comes into contact with
What is astatine?
A radioactive halogen that decays rapidly - it is predicted to be the least reactive halogen
How is the trend in reactivity of the halogens explained down the group?
- Atomic radius increases
- More inner shells so shielding increases
- Less nuclear attraction to capture an electron from another species
- Reactivity decreases
What does the power of oxidising agent do down the halogen group?
Decreases - they become weaker oxidising agents down the group
What is a disproportionation reaction?
A redox reaction in which the same element is both oxidised and reduced
How does chlorine react with water?
Cl2 (aq) + H2O (l) -> HClO (aq) + HCl (aq)
What type of reaction is the reaction of chlorine with water?
Disproportionation reaction
What is the reaction of chlorine with cold, dilute aqueous sodium hydroxide?
Cl2 (aq) + 2NaOH (aq) -> NaClO (aq) + NaCl (aq) + H2O (l)
What type of reaction is chlorine with cold, dilute aqueous sodium hydroxide?
Disproportionating reaction
How is water purified from its reaction with chlorine?
The bacteria in the water are killed by the chloric acid and chlorate ions produced in the reaction
What can chloric acid act as?
A weak bleach
What are the risks of chlorine use in water purification?
Chlorine gas in extremely toxic and chlorine can be a respiratory irritant in small concentrations, and large concentrations can be fatal. It can also react with organic hydrocarbons such as methane. This forms chlorinated hydrocarbons which are suspected of causing cancer
What are the benefits of using chlorine in water purification
The quality of drinking water would be compromised without use of chlorine. Diseases such as typhoid and cholera might breakout. The benefits of chlorine easily outweigh the risks
