inorganic chemistry and the periodic table Flashcards
group 7 name
characteristics
halogens
diatomic molecules
Why are fluorine and astatine generally ignored out of the halogens?
Fluorine behaves differently to rest of elements and astatine only exists as a radioactive isotope
trend in state down group 7
gas to solid
trend in mp/bp down group 7
increases
trend in electronegativities down group 7
decreases
how London forces are formed between diatomic halogen molecules
identical atoms mean pair of electrons are shared equally between (therefore on average aren’t polar). fluctuations in charge result in a temporary dipole. if molecule on left forms an instantaneous dipole, another dipole is induced on right, producing a force of attraction (instantaneous dipole-induced dipole attraction).
trend in bond strength between atoms in group 7
increases as number of electrons in molecules increases
properties determining electronegativity of an atom
nuclear charge
distance between nucleus and bonding pair
shielding effect
trend in reactivity down group 7
decreases down group w electronegativity
roles of halogens in reactions
act as oxidising agents, gaining electrons to form a negative ion.
due to high electronegativity
most vigorous reactions between group 1 and 2 metals with halogens
elements at bottom of groups 1 and 2 with elements at top of group 7
products of group 1 and 2 metals w halogens
reaction process
salts
ionic salts that are usually white
redox reactions in which halogen acts as oxidising agent
oxidation numbers in reaction between group 1 and 2 metals w halogens
halogen decreases from 0 to -1
metal increases from 0 to +1/+2
way to make halide colors more distinctive
add an organic solvent such as cyclohexane as halogens are more soluble than in water so will dissolve in upper layer where colors will be more distinctive
color of chlorine / bromine/ iodine
Cl» green
Br» orange brown
I»_space; purple
why is chlorine most reactive of halogens?
atom is smaller so outer electrons are closer to nucleus
smallest amount of shells and so shielding is reduced
disproportionation
a reaction in which one element undergoes both oxidation and reduction simultaneously.
reaction of chlorine with water
forms chloric acid and hydrochloric acid
Cl2 +H2O»_space; HCl + HCLO
reaction of chlorine with cold alkali
forms salts of the chloric and hydrochloric acids
sodium chloride and sodium chlorate 1
eg, 2NaOH + Cl2»_space; NaCl + NaClO + H2O
sodium chlorate use
disinfectant, used as main ingredient of bleach.
reaction of chlorine with hot alkali
forms salts of chloride and chlorate 5
eg, 6NaOH + 3Cl2»_space; 5NaCl + NaClO3 + 3H2O
how do halide ions differ from halogen molecules in their reactions
halide ions act as reducing agents in reactions while halogen molecules act as oxidising agents.
reducing power of halide ions as you go down the group
increases
oxidising power of halogen molecules as you go down the group
decreases
sulfuric acid role in reactions
can act as an oxidising agent and an acid
partially ionising : H2SO4»_space; H+ + HSO4
HSO4-»_space; H+ + SO42-
3 possible reaction products with sulfuric acid
sulfur dioxide
sulfur
hydrogen sulfide
observation and products in reaction of NaCl w conc. H2SO4
misty fumes and hydrogen chloride is formed
observation and products in reaction of NaBr w conc. H2SO4
misty fumes, brown fumes and colourless gas w choking smell
HBr, Br2, SO2
observation and products in reaction of NaI w conc. H2SO4
misty fumes, purple fumes/black solid, colourless gas w choking smell, yellow solid, colourless eggy gas
HI, I2, SO2, S, H2S
role of sulfuric acid in halogen reactions
NaCl» behaves as an acid as Cl has low reducing power
NaBr» is reduced as Br has more reducing power
NaI»_space; greater reducing power of iodide ions reduces sulfuric acid fully
equation of reaction of sulfuric acid w sodium chloride
NaCl + H2SO4»_space; NaHSO4 + HCl
equation of reaction of sulfuric acid w sodium bromide
made up of 2 redox reactions:
2Br-»_space; Br2 + 2e- // H2SO4 + 2H+ +2e-»_space; 2H2O + SO2
2HBr + H2SO4»_space; 2H2O + SO2 + Br2
equation of reaction of sulfuric acid w sodium iodide
3 redox reactions occur, put together
6HI + H2SO4»_space; 4H2O + S +3I2
precipitate colour of halogens in addition of silver nitrate
Cl»_space; white
Br» cream
I» yellow
Which halogen does dilute aqueous ammonia test for
bromide and iodide ions as they are insoluble
which halogen does concentrated aqueous ammonia test for
Iodide ions as they are insoluble
Why do halide precipitates dissolve in the ammonia solutions?
formation of a complex ion
hydrogen halides reaction with water
form colourless, acidic solutions
why is the formation of hydrofluoric acid from hydrogen fluoride and water reversible?
because it is a weak acid
reaction of water and hydrogen iodide
forms hydriodic acid
equation for reaction of HCl with water
H2O + HCl»_space; H3O + Cl-
reactions of hydrogen halides with ammonia gas
form white ionic solid salts
eg, NH3 + HCl»_space; NH4Cl
