Chapter 8 - Group 2 and Halogens Flashcards
physical properties of group 2 metals?
- high melting points
- light
- low densities
- form colourless white compounds (precipitates)
explain the reactivity trend down group 2
increases
- an electron at a higher energy level
- thus larger atomic radius
- less nuclear attraction
- easier to lose electrons
redox reactions of group 2?
are reducing agents
- are oxidised themselves
- lose electrons
redox reaction with oxygen of group 2?
react vigorously to from a form metal oxide
how does magnesium react with oxygen?
magnesium burns with a brilliant white light and forms a white precipitate
group 2 reaction with water? is it a redox reaction?
all except beryllium react
- form hydroxides
- hydrogen gas also formed
- yes, redox
group 2 reaction with dilute acid? is it redox?
- form a soluble salt
- and hydrogen
- yes, redox
explain the trend in ionisation energy down group 2?
- decreases
- larger atomic radius
- more electron sheilding
- less nuclear attraction
- electrons easily lost
group 2 oxide reaction with water?
- release hydroxide ions
- form alkaline solutions
- metal hydroxide
- when saturated, will form a white precipitate
trend in the solubility of group 2 hydroxides down the group?
increases, as they release more OH- ions as you go down, making the solution more alkaline
state the uses of group 2 compounds as bases? elaborate later
- agriculture
- medicine
- construction
describe how group 2 compound bases are used in agriculture?
- calcium hydroxide used as ‘lime’ by farmers
- reduces the acidity of the soil
describe how group 2 compound bases are used in medicine? why is it safe to swallow?
- indigestion = too much hydrochloric acid in stomach
- magnesium hydroxide neutralises excess stomach acid
- ‘milk of magnesia’
- not concentrated
describe how group 2 compound bases are used in construction? DRAWBACK OF USAGE?
calcium carbonate present in limestone and marble
- use din manufacture of glass and steel
- DRAWBACK readily react with acid causing acid rain
general physical properties of group 17 halogens?
- low melting and boiling point
- exist as diatomic molecules
why does the boiling point increase as you go down group 17?
- more electrons
- stronger London forces
- more energy required to break the IMF
- boiling point increases
appearance of each halogen at RTP?
- fluorine: pale yellow gas
- chlorine: pale green gas
- bromine: red-brown liquid
- iodine: shiny grey-black solid
- astatine: never been seen
electron configuration of group 17 elements?
7 outer shells
- 2 in s subshell
- 5 in p subshell
- in p block
redox reactions of group 17?
are oxidising agents
- reduced themselves
purpose of displacement reactions of halogens with halides?
show that reactivity decreases down the group
method for halogen-halide displacement reaction?
- solution of halogen added to an aqueous solution of another halide
- reaction take place
- solution colour changes
what do we do to bromine and iodine in the displacement reaction and why?
because iodine and bromine appear simliar in colour in solution with water, they are added cyclohexane
why does the step taken for bromine and iodine work?
- cyclohexane is a non-polar organic solvent
- halogens are non-polar
- COLOURS much easier to tell apart
- iodine: orange
- bromine: deep violet
results of halogen-halide displacement reaction?
- chlorine reacts with both Br- and I-
- bromine only with I-
- iodine doesn’t react at all
explain the trend of reactivity down group 17
- atomic radius increases
- more shielding
- less nuclear attraction with the electron of another species
- reactivity decreases
which is the stongest oxidising agent?
fluorine
what is a disproportionation reaction?
- redox reaction in which the same element is both oxidised and reduced
reaction of chlorine with water? equation and products?
- disproportionation reaction occurs
- chlorine + water -> chloric (I) acid + hydrochloric acid
uses of chlorine + water reaction, test afterwards?
chloric (I) acid AND chlorate (I) ions kill bacteria
- weak bleach, litmus paper red (acidic), then bleached
the reaction of chlorine + cold dilute aqueous sodium hydroxide?
- disproportionation reaction
- by itself, chlorine not very soluble
- with NaOH much more dissolves
- chlorate (I) from sodium chlorate produced
benefits and risks of chlorine usage?
+ purifies water
+ rids it from typhoid, cholera
- toxic gas
- respiratory irritant in low concentrations
- fatal in large concentrations
- can react with organic compounds like methane, suspected of causing cancer
redox ability of halogens and halide ions? which one cannot reduce and which one CAN?
halogens- oxidising agents
halide ions- reducing agents
- can be shown by reading with sulfuric acid, halides oxidised to form halogens
- HOWEVER, chlorine atoms cannot, bromide ions and iodide ions can
carbonate test?
- add any dilute acid
- bubbles of CO2 produced
- tets with ilmewater
- white precipitate of carbonate
sulfate test?
- add barium nitrate/chloride
- white precipitate of barium sulfate
halide test?
- add aqueous silver nitrate
- different colour precipitate
- chloride: white
- bromide: cream
- iodide: yellow
what additional test after halide test? why?
- add ammonia solution
- chlorine dissolves in all concentrations
- bromine dissolves in concentrated solutions
- iodine in no concentration
order of ion tests and why?
- carbonate, sulfate, halide
- all precipitates white
- will give false positive results
test for ammonium ion?
- add aqeous sodium hydroxide
- ammonia gas produced
- mixture WARMED
- gas released
observation/further tests during ammonium ion test? PRECAUTION?
- ammonia gas produced
- BUT
- won’t see gas bubbles because ammonia very soluble
- smells burnt and fleshy
- alkaline so turns litmus paper blue
- HAZARDOUS, test with care
