halogens Flashcards
what are halogens
group 17 the most reactive nonmetals
exist as diatomic molecules
what are examples of halogens
Fluorine (F2): very pale yellow gas. It is highly reactive
Chlorine : (Cl2) greenish, reactive gas, poisonous in high concentrations
Bromine (Br2) : red liquid, that gives off dense brown/orange poisonous fumes
Iodine(I2) : shiny grey solid turns to purple gas
what are trends in melting and boiling points down a group
increases down the group
As the molecules become larger they have more electrons and so have larger induced dipole-dipole forces
(London forces) between the molecules. As the intermolecular forces get larger more energy has to be put into break these intermolecular forces. This increases melting and boiling point
what’s the electron configuration of group 17
All group 7 elements have the outer shell s2p5 electron configuration.
The will often react by gaining of one electron in redox reactions to form 1–ions
why does the reactivity of halogens decreases down the group
because atoms get bigger with more shielding so they less easily attract and accept electrons. They therefor form -1 ions less easily down the group
what is the halogen halide displacement reaction
a solution of each halogen is added to aqueous solutions of the other halides.
what happens if the halogen is more reactive than the halide present
a reaction takes place, the halogen displacing the halide from the solution.
the solution changes colour
how can you tell apart the solution of iodine and bromine in water when they appear a similar orange brown colour depending on the concentration
an organic non polar solvent such as cyclohexane can be added and the mixture shaken
The non polar halogens dissolve more readily in cyclohexane than in water
In cyclohexane their colours are much easier to tell apart with
Iodine being deep violet.
what are the colours of halogen solutions in water
chlorine –> pale green
bromine –> orange
iodine –> brown
what are the colours of halogens in cyclohexane
the top layers for :
chlorine—> pale green
bromine—> orange
iodine —> violet
whats the reaction of chlorine with bromide ions
Cl2(aq) + 2NaBr(aq) —-> 2NaCl(aq) + Br2(aq)
Ionic equation
Cl2(aq) +2Br(aq) —-> 2Cl-(aq) + Br2(aq)
0 —–> -1 REDUCTION
-1 —–> 0 OXIDATION
what are the results from the halogen displacement reaction
chlorine has clearly reacted with both Br- and I-
e.g Cl2(aq) + 2Br(aq) —-> 2Cl-(aq) + Br2(aq)
bromine has only reacted with I- only
e.g Br2(aq) + 2I- —-> 2Br-(aq) + I2(aq)
iodine has not reacted at all
whats the reactivity between chlorine to bromine
chlorine most reactive than bromine than iodine is the least reactive
Whats the explanation of reactivity
Chlorine is more reactive than bromine because it will
gain an electron and form a negative ion more easily than
bromine. The is because an atom of chlorine is smaller
than bromine and the outermost shell of chlorine is less
shielded than bromine so the electron to be gained is
attracted more strongly to the nucleus in chlorine than bromine
what about fluorine
is a pale yellow gas reacting with almost any substance that comes into contact with the
what about astatine
is extremely rare because its radioactive and decays rapidly
predicted to be least reactive halogen
what is the strongest oxidising agent in the halogens
fluorine because its gaining electrons from other species more rapidly than the other halogens. The halogens become weaker oxidising agents down the group
what is disproportionation
is a redox reaction in which the same element is both oxidised and reduced. The reaction of chlorine with water and with cold dilute sodium hydroxide are two examples of disproportionation reaction
what happens during the reaction with chlorine and water
disproportionation reaction takes place
show the reaction between chlorine and water
Cl2(aq) + H20(l)——> HCl(aq) + HCL (aq)
0 —–> -1 REDUCTION
0 —–> +1 OXIDATION
what is chlorine used as
Chlorine is used in water treatment to kill bacteria. It has been used to treat drinking water and the water in
swimming pools. The benefits to health of water treatment by chlorine by its killing of bacteria outweigh its risk of toxic effects and possible risks from formation of chlorinated hydrocarbons
the product of the reaction between water and chlorine should produce acids how can we prove this
If some universal indicator is added to the
solution it will first turn red due to the acidity
of both reaction products. It will then turn
colourless as the HClO bleaches the colour
what is bacteria killed by from the water and chlorine reaction
chloric acids and chlorate ions ClO-
what can chloric acid act as
a weak bleach
what happens in the reaction between chlorine with dilute NaOH solution
Cl2,(and Br2, I2) in aqueous solutions will react with cold sodium hydroxide. The chlorine is reacting by disproportionation. The colour of halogen solution will fade to colourless
show the reaction of chlorine with dilute NaOH solution
Cl2(aq) + 2NaOH(aq) —–> NaClO(aq) + NaCl(aq) +H2O
0 —–> -1 REDUCTION
0 —–> +1 OXIDATION
what is the use of the products formed from chlorine with dilute NaOH solution
The mixture of NaCl and NaClO (sodium chlorate (I)) is used as Bleach and to disinfect/ kill bacteria
what are the benefits of chlorine use
beneficial in ensuring our water is afe to drink and that bacteria is killed
what are risks of chlorine use
chlorine is a respiratory irritant in small concentrations and large concentrations can be fatal
what happens in the test for halides
This reaction is used as a test to identify which halide ion
is present. The test solution is made acidic with nitric
acid, and then Silver nitrate solution is added drop wise
show the reaction of the test of halides
Ag+(aq) + X-(aq) —–> AgX(s)
when chlorine bromine and iodine are used in the test of halides what percipitate is formed
Fluorides produce no precipitate
Chlorides produce a white precipitate
Ag+(aq) + Cl- (aq) AgCl(s)
Bromides produce a cream precipitate
Ag+(aq) + Br- (aq) AgBr(s)
Iodides produce a pale yellow precipitate
Ag+(aq) + I- (aq) AgI(s)
what is the role of nitric acid
The role of nitric acid is to react with any carbonates
present to prevent formation of the precipitate
Ag2CO3. This would mask the desired observations
2 HNO3 + Na2CO3 2NaNO3 + H2O + CO2
how can we differentiate the colours of the silver halide percipitates
can be treated with ammonia
Silver chloride can be dissolves in dilute ammonia to form complex ion
AgCl(s) + 2NH3(aq) [Ag(NH3)2]+ (aq) + Cl- (aq)
colourless solution
Silver bromide dissolves in concentrated ammonia to form a complex ion
AgBr(s) + 2NH3(aq) [Ag(NH3)2]+ (aq) + Br- (aq)
Colourless solution
Silver iodide does not react with ammonia– it is too insoluble.
Bromine is used to extract iodine from a solution containing iodide ions what’s the ionic equation for this reaction
Br2 + 2I^- —-> I2 + 2Br-
Bromine can extracted by bubbling chlorine gas through concentrated solution containing bromide ions . Write the ionic equation
Cl2 + 2Br^- ——>2Cl + Br1
