The halogens Flashcards
in which block are the halogens
p-block
state and colour of fluorine
pale yellow gas
state and colour of chlorine
green gas
state and colour of bromine
red-brown liquid
state and colour of iodine
black solid
what factors increase down group 7
- nuclear charge
- number of e-
- atomic radius
- boiling point
why does the boiling point of the halogens increase down the group
- more electrons moving down the group, strength of the temporary dipoles increases.
- Increased dipoles mean greater London forces
what type of reactions are halogens often involved in
- redox reactions
- they gain 1 e- to form 1- halide ion
why does electronegativity decrease down group 7
- increase in atomic radii
- shielding outweighs the increase in nuclear charge
- less attraction between nucleus and valent e-
why is fluorine the most reactive
- atomic radius increases down the group
- greater shielding
- less nuclear attraction to attract an electron from another species
what happens when a more reactive and less reactive halogen react
- more reactive halogen will displace a less reactive halide ion from solution resulting in a colour change corresponding to the displaced halogen
why are halogens less reactive down group 7
- decreasing electronegativity reduces halogen’s ability to attract and e- to form 1- ion
what can be done to make colour change in displacement reactions easier to see
- in a separating funnel, shake the reaction mixture with an organic solvent like hexane
- non-polar halogen dissolves in non-polar organic solvent
- polar halide dissolves in aq layer
- organic layer above aq
what colour is chlorine in water
pale green
what colour is bromine in water
orange
what colour is iodine in water
brown
in non-polar organic solvent chlorine is
pale yellow-green
in non-polar organic solvent iodine is
purple
in non-polar organic solvent bromine is
yellow-orange
ionic equations for displacement reactions
X2 (aq) + 2Y- (aq) –> Y2(aq) + 2X- (aq)
- the more reactive species ends up as ions
are halogens oxidising or reducing agents
they’re oxidising agents and become reduced themselves
define disproportionation
when a single element is simultaneously oxidised and reduced in a reaction
equation for the disproportionation of chlorine when reacted with water
Cl2(aq) + H2O(l) —> HCl (aq) + HClO(aq)
- Cl reduced from 0 in Cl2 to -1 in HCl
- Cl oxidised from 0 in Cl2 to +1 in HClO
why is chlorine used in water purification
on addition to water, the products, chloric (I) acid, HClO, and the Cl- ion, effectively kill bac
advantages of chlorinating water
- sanitises water by killing bac
- prevents the spread of waterborne diseases
disadvantages of chlorinating water
- may react with hydrocarbons to form carcinogenic chlorinated hydrocarbons
- Cl2 is a toxic gas and can irritate the respiratory system in low conc
what kind of reaction occurs when chlorine reacts with cold, dilute NaOH and give the equation
- disproportionation
- Cl2(g) + 2NaOH(aq) —> NaCl(aq) + NaClO(aq) + H2O(l)
- 0 in Cl2 to -1 in NaCl and +1 in NaClO
- NaClO is the active ingredient in bleach
test for halides
- add AgNO3
- Cl- produces white ppt (AgCl)
- Br- produces cream ppt (AgBr)
- I- produces yellow ppt (AgI)
silver halides can be hard to distinguish so what’s is added to distinguish them clearly
NH3
how can you tell if ppt is AgCl
soluble in dilute NH3
how can you tell if ppt is AgBr
soluble in conc NH3
how can you tell if ppt is AgI
insoluble in conc NH3
