halogens Flashcards
what colour is fluorine?
very pale yellow gas - highly reactive
what colour is chlorine?
greenish, reactive gas - poisonous in high concentrations
trend in melting point down the group
increases down the group, as the molecules become larger they have more electrons and so have larger london forces between the molecules. as the intermolecular forces get larger, more energy has to be put in to break the forces
trend in electronegativity down the grou[
decreases down the group
atomic radii increases down the group due to the increasing number of shells. the nucleus is therefore less able to attract the bonding pair of electrons
electronegativity
relative tendency of an atom in a molecule to attract electrons in a covalent bond to itself
reactivity down the group
decreases down the group as the atoms get bigger with more shielding so they less easily attract and accept electrons. they therefore form -1 ions less easily down the group
oxidation reactions of halide ions by halogens
a halogen that is a strong oxidising agent will displace a halogen that has a lower oxidising power from one of its compounds
oxidising strength down group
decreases, oxidising agents are electron acceptors - more shielding makes it harder to attract electrons
chlorine and potassium chloride
very pale green solution, no reaction
bromine and potassium chloride
yellow solution, no reaction
iodine and potassium chloride
brown solution, no reaction
chlorine and potassium chloride
yellow solution, Cl has displaced Br
bromine and potassium bromide
yellow solution, no reaction
iodine and potassium bromide
brown solution, no reaction
potassium iodide and chlorine
brown solution, Cl has displaced I
potassium iodide and bromine
brown solution, Br has displaced I
potassium iodide and iodine
brown solution, no reaction
potassium chloride (organic) and chlorine
colourless, no reaction
potassium chloride (organic) and bromine
yellow, no reaction
potassium chloride (organic) and iodine
purple, no reaction
potassium bromine (organic) and chlorine
yellow, Cl has displaced Br
potassium bromide (organic) and bromine
yellow, no reaction
potassium bromide (organic) and iodine
purple, no reaction
potassium iodide (organic) and chlorine
purple, Cl has displaced I
potassium iodide (organic) and bromine
purple, Br has displaced I
potassium iodide (organic) and iodine
purple, no reaction
chlorine in organic solvents
colourless
bromine in organic solvents
yellow
iodine in organic solvents
purple
disproportionation
name for a reaction where an element simultaneously oxidises and reduces
reaction of halogens with cold, dilute NaOH solution
e.g. Cl2 (aq) + 2NaOH (aq) = NaCl (aq) + NaClO (aq) + H2O (l)
same for I2 and Br2
what is the mixture of NaCl and NaClO used for?
bleach and to disinfect/kill bacteria
reactions of halogens with hot dilute NaOH
e.g. 3Cl2 (aq) + 6NaOH (aq) = 5NaCl (aq) + NaClO3 (aq) + 3H2O (l)
same for I2 and Br2
NaClO name
sodium chlorate (I)
NaClO3 name
sodium chlorate (V)
K2SO4 name
potassium sulfate (VI)
K2SO3 name
potassium sulfate (IV)
reducing agents down the group
increasing power down group
explanation of differing reducing power of halides
reducing agent donates electrons
reducing power increase down group
greater tendency to donate electrons
because ions get bigger, it is easier for the outer electrons to be given away as the pull from the nucleus on them becomes smaller
reaction of halide ions with silver nitrate is to test for what
identify which halide ion is present.
what is the role of nitric acid
react with any carbonates present to prevent formation of the precipitate Ag2CO3. this would mask the descired observation
what colour does chloride produce + ionic equation
white precipitate Ag+ (aq) + Cl- (aq) = AgCl (s)
what colour does bromide produce + ionic equation
cream precipitate Ag+ (aq) + Br- (aq) = AgBr (s)
what colour does iodide produce + ionic equation
pale yellow precipitate Ag+ (aq) + I- (aq) = AgI (s)
effect of light on silver halides
the precipitates (except AgI) darken in sunlight formng silver. this reaction is used in photography to form the dark bits on photographic film
effect of ammonia on silver halides
silver halide precipitates can be treated with ammonia solution to help differentiate between them if the colours look similar
in what does silver chloride dissolve in to form a complex ion?
AgCl (s) +2NH3 (aq) = [Ag(NH3)2]+ (aq) + Cl- (aq)
dissolves in DILUTE ammonia
in what does silver bromide dissolve in to form a complex ion?
AgBr (s) +2NH3 (aq) = [Br(NH3)2]+ (aq) + Br- (aq)
dissolves in CONCENTRATED ammonia
in what does silver iodide dissolve in to form a complex ion?
nothing, doesn’t react with ammonia - too insoluble
hydrogen halides solubility in water
all soluble in water, they dissolve to form acidic solutions
e.g. HCl (g) + H2O = H3O+ (aq) + Cl- (aq)
what is produced when hydrogen halides react readily with ammonia
white smoke
e.g. HCl (g) + NH3 (g) = NH4Cl (s)
