2.2 group 2 and group 7 Flashcards by Evie Ravenscroft

what happens to atomic radius down group 2?

gets larger
extra electron shells are added

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what happens to first ionisation energy down group 2?

decreases down the group
as atomic radius increases
electron shielding increases
so nuclear attraction for outer electrons decreases
so outer electrons are easier to remove

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what happens to reactivity down group 2?

increases
as atomic radius increases
electron shielding increases
so nuclear attraction for outer electrons decreases
so outer electrons are easier to lose

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what happens to melting point down group 2?

decreases
same charge on metal ions and same no of delocalised electrons
but atomic radius and electron shielding increase
so nuclear attraction for delocalised electrons decreases
so less energy needed to overcome strong metallic bonds

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what happens to electronegativity down group 2?

decreases
atomic radius increases
electron shielding increases
so nuclear attraction for outer electrons decreases
so ability to attract pair of electrons in a covalent bond decreases

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reaction of group 2 metals with water

oxidised from state of 0 to +2
metal + water -> metal hydroxide + hydrogen
react more readily down group as ionisation energy decreases

(but mg and steam makes metal oxide and h)

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solubility of group 2 compounds

metal hydroxide (OH-) - more soluble down group

metal sulfate (SO4^2-) - less soluble down group

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test for sulphate ions

add dilute HCl then barium chloride and presence of sulphate ions causes white precipitate of barium sulphate to form
(barium sulphate is insoluble)

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use of barium sulphate because its insoluble. why is it good that its insoluble?

barium meal
swallowed by patient and it coats tissues in oesophagus/ stomach/ intestine so they show up on x-ray
other barium compounds cant be used as theyre soluble. barium sulphate isnt so cant be absorbed by cells so isnt harmful

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use of magnesium

extracting titanium from its ore
titanium oxide is converted to titanium chloride by heating with carbon in steam of chlorine gas.
TiO2+ 2C + 2Cl2 -> TiCl4 + 2CO
titanium chloride then purified by fractional distillation then reduced by magnesium in furnace
TiCl4 (aq) + 2Mg (l) -> Ti (s) + 2MgCl2 (l)

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removing sulfur dioxide from flue gases

mix calcium oxide or calcium carbonate with water to make an alkaline slurry
this is sprayed on flue gases and reaction occurs producing solid calcium sulfite

CaO(s)+2H20(l) +S02(g) ->CaSO3(s) +2H20(l)

CaCO3(s)+2H2O(l)+SO2(g)-> CaSO3(s)+2H2O (l)+C02(g)

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What are group 2 metals used for as they are alkali?

neutralising acids
calcium hydroxide used in agriculture to neutralise acidic soils
magnesium hydroxide is used in indigestion tablets as an antacid

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fluorine, chlorine, bromine and iodine colour, state, reactivity and uses?

Fl2- pale yellow gas, making plastics
Cl2- green gas, bleach and disinfectant
Br2- red brown liquid, testing saturation and water purification
I2- grey solid, antiseptic, mineral suppliment
all very reactive

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what happens to boiling point down group 7?

increases
increased atomic radius, increased van der waals between molecules, more energy to break IMF

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what happens to electronegativity down group 7?

decreases
atomic radius increases, more inner electron shielding, weaker attraction between nucleus and pair of electrons in a covalent bond

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what happens to 1st ionisation energy down group 7?

decreases
increased atomic radius
more inner electron shielding
so weaker attraction from nucleus to electrons in outer shell

are halide ions oxidising or reducing agents? what happens to this down the group?

reducing (they have gained an electron to become ions so are losing electrons when reducing)
more reducing down group as atoms get larger and outer shell further from nucleus so easier to lose electrons

displacement reactions for group 7- draw the table

page 158 of text book

MAKE FLASHCARDS FOR PAGE 159

Just read it

how do you make bleach?

mix chlorine gas with cold, dilute sodium hydroxide at room temp and you get sodium chlorate (1)
2NaOH(aq) + Cl2(g) -> NaClO(aq) + NaCl(aq) +H2O(l)

what is a disproportionation reaction?
eg?

one element is both oxidised and reduced
when making bleach, chlorine is oxidised and reduced

reaction of chlorine and water

disproportionation and you get chloride and chlorate (1) ions
Cl2(g) +H2o (l) <->2H+(aq) + Cl-(aq) + ClO- (aq)

normal eq: Cl2(g) + H2O(l) <-> HCl(aq) + HClO(aq)

reaction of chlorine and water under uv light

Cl2(g) +H2O(l) <-> 2H+(aq) + 2Cl- (aq) + 1/2 O2(g)

No chlorate ions produced so not effective at killing bacteria

why can we use chlorine to treat water?

chlorate (1) ions produced when react with water and this kills bacteria so its safe to drink/ swim
but
chlorine is toxic

benefits of using chlorine to treat water

kills disease causing microorganisms (and some chlorine stays in water preventing reinfection further down supply) prevents growth of algae eliminates bad taste and smells removes discolouration caused by organic compounds

limitations of using chlorine to treat water what is the big BUT?

chlorine gas harmful if breathed in- irritates resp system liquid chlorine on skin or in eyes can cause severe chemical burns chlorine reacts with variety of organic compounds in water to form chlorinated hydrocarbons which can be carcinogenic BUT risks of untreated water (eg cholera epidemic) are worse than risks of chlorine

are halogens oxidising or reducing agents? what happens to this down the group?

oxidising agents (they gain an electron) decreases down the group as atomic radius gets larger so more shielding so less nuclear attraction for outer electrons

reaction of halides with concentrated sulfuric acid

hydrogen halide produced then what happens next depends on halide- some strong enough reducing agents that they reduce sulfuric acid to sulfur dioxide and water. iodine is such a strong reducing agent it can reduce sulfur dioxide to H2S or S

general equations and half equations for reaction of halides with concentrated sulfuric acid

NaX + H2SO4 -> NaHSO4 + HX 2HX + H2SO4 -> X2 + SO2 + 2H2O 2X- (g) -> X2(s) + 2e- (halide oxidised) H2SO4 + 2H+ + 2e- -> SO2 + 2H2O (sulfuric acid reduced)

What are the equations and observations of the reactions of halide ions with concentrated sulfuric acid?

On a separate poster (make sure to look)

how do you test for halides?

add dilute nitric acid (not hcl due to chloride ions) to remove any ions which could interfere with the test add few drops of silver nitrate solution (AgNO3(aq)) and a precipitate of silver halide will form Ag+(aq) + X-(aq) -> AgX(s)

what colour are the precipitates that form in the halide test? how can we further distinguish them?

fluoride- no precipitate (silver fluoride soluble) chloride- white bromide- cream iodide- yellow add ammonia as they all have diff solubilities cl- dissolves in dilute NH3 br- dissolves in conc NH3 I- insoluble in NH3

how do you test for group 2 ions? 2 ways

1) flame test- dip wire loop in conc hcl to clean then into compound then hold in flame Ca2+ brick red, Sr2+ red, Ba2+ pale green 2) add dilute NaOH dropwise and observe precipitate keep adding in excess and record changes

precipitates formed from group 2 ions with NaOH then excess NaOH

Mg2+ slight white then white Ca2+ slight white then slight white Sr2+ slight white then slight white Ba2+ no change then no change

test for ammonium ions equation of ammonium to ammonia gas

add hydroxide ions (in form of dilute NaOH) to solution containing ammonium ions, ammonia gas produced NH4+(aq) + OH-(aq) -> NH3(g) + H2O(l) ammonia gas is alkaline so can gently heat then test with damp red litmus paper- goes blue

what is the test for sulfate ions? equation?

dilute HCl (get rid of carbonate and sulfate ions what would confuse the results and cant use sulfuric acid because of sulfate ions) the barium chloride and white precipitate of barium sulfate forms Ba^2+(aq) + SO4^2-(aq) -> BaSO4(s)

what is the test for hydroxide ions?

they make a solution alkaline so use pH indicator eg red litmus paper goes blue

what is the test for carbonate ions? equation of carbonate ions and hydrogen

add dilute HCl and it will fizz as carbonate ions react w H ions in acid to give CO2 CO3^2-(aq) + 2H+(aq) -> CO2(g) + H2O(l) test for CO2 by bubbling gas through limewater and it will go cloudy