The Halogens Flashcards
what type of molecules do the halogens exist as?
diatomic molecules
what happens to the boiling point of halogens when you go down the group?
boiling point increases
why does the boiling point increase as you go down group 7?
- the number of electrons increases as you go down the group
- there are stronger London forces as you go down the group
- more energy is required to overcome the intermolecular forces
what is the outer shell electron configuration of halogens?
s2, p5
are halogens reduced or oxidised?
reduced, gains one electron to form 1- ions
what is the trend in reactivity down group 7?
reactivity decreases
why does reactivity decrease as you go down group 7?
- atomic radius increases
- electron shielding increases
- nuclear attraction weakens
- greater nuclear charge
- harder to gain one electron
what are displacement reactions?
when the most reactive halogen replaces the least reactive halogen in a reaction
what is a disproportionation reaction?
a redox reaction in which the same element is both oxidised and reduced
what are some examples of disproportionation reactions?
- the reaction of chlorine and water (used in water treatment)
- the reaction of chlorine with cold, dilute aqueous sodium hydroxide (used to form bleach)
what is the equation for the reaction of chlorine and water?
Cl2(aq) + H2O(l) - >HClO(aq) + HCl(aq)
what is the equation for the reaction of chlorine with cold, dilute aq NaOH?
Cl2(aq) + 2NaOH(aq) -> NaClO(aq) + NaCl(aq) + H2O(l)
what are the benefits of chlorine use?
killing bacteria in water treatment
what are the risks of chlorine use?
- extremely toxic gas
- chlorinated water reacts with organic hydrocarbons (from decaying vegetation) forming chlorinated hydrocarbons = suspected of causing cancer
what is the evidence for the boiling point increasing as you go down group 7?
the density increases
why is chlorine with water a disproportionation reaction?
- chlorine is oxidised
–> Cl2(0) to HClO(+1) - chlorine is reduced
–> Cl2(0) to HCl(-1)
why is the reaction with chlorine and cold, dilute aq sodium hydroxide a disproportionation reaction?
- chlorine is oxidised
–> Cl2(0) to NaClO(+1) - chlorine is reduced
–> Cl2(0) to NaCl(-1)
when answering questions about the decisions on whether or not the chlorinated water should be used?
- balance the strengths and weaknesses, ethical considerations as people have the right to choose
what is the colour of chlorine in water?
- pale green
what is the colour of bromine in water?
- orange
what is the colour of iodine in water?
- brown
what is the colour of chlorine in cyclohexane (top layer)?
- pale green
what is the colour of bromine in cyclohexane (top layer)?
- orange
what is the colour of iodine in cyclohexane (top layer)?
- violet
