topic 4: inorganic chemistry and the periodic table Flashcards
what happens to the atomic radius down group 2
increases because one goes down the group, the atoms have more shells of electrons making the atom bigger
what happens to the melting point down group 2
down the group the melting points decrease
- the metallic bonding weakens as the atomic size
increases
- the distance between the positive ions and delocalized electrons increases
- therefore the electrostatic attractive forces between the positive ions and the delocalized electrons weaken
what happens to the 1st ionisation energy down group 2
the outermost electrons are held more weakly because they are successively further from the nucleus in additional shells. in addition, the outer shell electrons become more shielded from the attraction of the nucleus by the
repulsive force of inner shell electrons
what happens to the reactivity down group 2 and why
the reactivity increases down the group as the atomic radii increase
- there is more shielding
- the nuclear attraction decreases and it is easier to remove (outer) electrons and so cations form more easily
- first ionisation energy decreases
- there is a increase in repulsion between the filled inner shells and the electrons removed
group 2 + oxygen
the group 2 metals will burn in oxygen. Mg burns with a bright white flame
2Mg + O2 —> 2MgO
MgO is a white solid with a high melting point due to its ionic bonding
group 2 + Cl2
The group 2 metals will react with chlorine
Mg + Cl2 —> MgCl2
Mg + steam
magnesium reacts in steam to produce magnesium oxide and hydrogen. the Mg would burn with a bright white flame
Mg (s) + H2O (g) MgO
Mg + warm water
giving a different magnesium hydroxide product
Mg + 2 H2O Mg(OH)2 + H2
other group 2 + cold water
react with cold water with increasing vigour down the group to form hydroxides
Ca + 2H2O(l) —> Ca(OH)2(aq) + H2 (g)
Sr + 2H2O(l)—> Sr(OH)2(aq) + H2(g)
Ba + 2H2O(l) —> Ba(OH)2(aq) + H2(g)
reactions of the oxides of group 2 elements with acids
MgO(s) + 2HCl(aq) —> MgCl2(aq) + H2O(l)
SrO(s) + 2HCl(aq) —> SrCl2(aq) + H2O(l)
CaO(s) + H2SO4(aq) CaSO4(aq) + H2O(l)
reactions of the hydroxides of group 2 elements with acids
2HNO3(aq) + Mg(OH)2(aq) —>Mg(NO3)2(aq) + 2H2O(l)
2HCl(aq) + Mg(OH)2(aq) —>MgCl2(aq) + 2H2O(l)
describe the solubility of group 2 hydroxides
group II hydroxides become more soluble down the group. all Group II hydroxides when not soluble appear as white precipitates
state the solubility of magnesium hydroxide
insoluble in water
describe solubility of calcium hydroxide
reasonably soluble in water
describe the solubility of barium hydroxide
easily dissolve in water
explain the solubility of group 2 sulfates
group 2 sulfates become less soluble down the group
which group 2 sulfate is the least soluble
BaSO4
what is thermal decomposition
the use of heat to break down a reactant into more than one product
thermal decomposition of group 2 carbonates
group 2 carbonates decompose on heating to produce group 2 oxides and carbon dioxide gas
MgCO3(s) —> MgO(s) + CO2(g)
what happens to the group 2 carbonates thermal decomposition down the group
become more thermally stable going down the group. as the cations get bigger they have less of a polarising effect and distort the carbonate ion less. the C-O
bond is weakened less so it less easily breaks down
what happens to the group 1 carbonates thermal decomposition
group 1 carbonates do not decompose with the exception of lithium. as they only have +1 charges they don’t have a big enough charge density to polarise the carbonate ion. lithium is the exception because its ion is small enough to have a polarising effect
Li2CO3(s) —> Li2O(s) + CO2(g)
test for thermal decomposition of carbonates
one is to heat a known mass of carbonate in a side arm boiling tube and pass the gas produced through lime water. time for the first permanent cloudiness to appear in the limewater. repeat for different carbonates using the same moles of carbonate/same volume of limewater/same Bunsen flame and height of tube above flame
thermal decomposition of group 2 nitrates
group 2 nitrates decompose on heating to produce group
2 oxides, oxygen and nitrogen dioxide gas. you would observe brown gas evolving (NO2) and the
white nitrate solid is seen to melt to a colourless solution and then re-solidify
2Mg(NO3)2 → 2MgO + 4NO2 + O2
describe the ease if thermal decomposition down the group
decreases
why does magnesium nitrate decompose the easiest
because the Mg2+ ion is smallest and has the greater charge density. it causes more polarisation of the nitrate anion and weakens the N―O bond
thermal decomposition of group 1 nitrates
group 1 nitrates, with the exception of lithium nitrate, do not decompose in the same way as group 2 nitrates. they decompose
to give a nitrate (III) salt and oxygen
2NaNO3 → 2NaNO2 + O2
4LiNO3 → 2Li2O + 4NO2 + O2
what is the method of a flame test
use a nichrome wire ( nichrome is an unreactive metal and will not give out any flame colour). clean the wire by dipping in concentrated hydrochloric
acid and then heating in blue roaring Bunsen flame. if the sample is not powdered then grind it up. dip wire in solid and put in blue roaring Bunsen flame and observe flame
what is the explanation for the occurrence of flame
in a flame test the heat causes the electron to move to a higher energy level. the electron is unstable at the higher energy level and so drops back down. as it drops back down from the higher to a lower energy level, energy is emitted in the form of visible light energy with the wavelength of the
observed light
what is the colour of lithium
scarlet red
what is the colour of sodium
yellow
what is the colour of potassium
lilac
what is the colour of rubidium
red
what is the colour of caesium
blue
what is the colour of magnesium
no flame colour
what is the colour of calcium
brick red
what is the colour of strontium
red
what is the colour of barium
apple green
describe the characteristics of fluorine (F2)
very pale yellow gas
it is highly reactive
describe the characteristics of chlorine (Cl2)
greenish
reactive gas
poisonous in high concentrations
describe the characteristics of bromine (Br2)
red liquid that gives off dense brown/orange poisonous fumes
describe the characteristics of iodine (I2)
shiny grey solid sublimes to purple gas
describe the trend in melting and boiling point of halogens (group 7) and why
increase 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 into break the forces. this increases the melting and boiling points
describe the trend of electronegativity for halogens
as one goes down the group the electronegativity of the
elements decreases. as one goes down the group the atomic radii increases due to the increasing number of shells. the nucleus is therefore less able to attract the bonding pair of electrons
describe the reactivity of halogens
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
what would chlorine displace
bromine and iodine
what does bromine displace
iodine
what does iodine displace
none
what are the different colour of the solution in the test tube which free halogen is present in solution
chlorine =very pale green solution (often colourless)
bromine = yellow solution
iodine = brown solution
what is the colour of the organic
solvent layer in the test tube
shows when each free halogen is
present in solution
chlorine = colourless
bromine = yellow
iodine = purple
reaction of halogens with cold dilute NaOH solution
Cl2(aq) + 2NaOH(aq) —> NaCl (aq) + NaClO (aq) + H2O(l)
the mixture of NaCl and NaClO is used as bleach and to disinfect/ kill bacteria
reaction of halogens with hot dilute NaOH solution
3Cl2 (aq) + 6NaOH(aq) —> 5 NaCl (aq) + NaClO3 (aq) + 3H2O (l)
what is the explanation of differing reducing power of halides
a reducing agent donates electrons.
the reducing power of the halides increases down group 7. they have a greater tendency to donate electrons because as the ions get bigger it is easier for the outer electrons to be given away as the pull from the nucleus on them becomes smaller
what happens in the reaction between chloride/fluoride ions and H2SO4
The H2SO4 is not strong enough an oxidising reagent to oxidise the chloride and fluoride ions. no redox reactions occur. only acid - base reactions occur
NaF(s) + H2SO4(l) —>NaHSO4(s) + HF(g)
observations: white steamy fumes of HF are evolved
NaCl(s) + H2SO4(l) NaHSO4(s) + HCl(g)
observations: white steamy fumes of HCl are evolved
describe the reaction between bromide and H2SO4
stronger reducing agents than Cl- and F- and after the initial acid- base reaction reduce the sulfur in H2SO4
from +6 to + 4 in SO2
observations: white steamy fumes of HBr are evolved. red fumes of bromine are also
evolved and a colourless, acidic gas SO2
what is the reaction between iodide and H2SO4
the strongest halide reducing agents. they can reduce the sulfur from +6 in H2SO4 to + 4 in SO2
, to 0 in S and -2 in H2S
NaI(s) + H2SO4(l) —> NaHSO4(s) + HI(g)
2HI + H2SO4 —> I2(s) + SO2(g) + 2H2O(l)
6HI + H2SO4 —> 3I2 + S(s) + 4H2O (l)
8HI + H2SO4 4I2(s) + H2S(g) + 4H2O(l)
observations:
white steamy fumes of HI are evolved. black solid and purple fumes of Iodine are also evolved. a colourless, acidic gas SO2. a yellow solid of Sulphur
H2S (Hydrogen Sulphide), a gas with a bad egg
smell
what is the test to identify the halide ions
nitric acid and silver nitrate solution
what is the role of nitric acid in the test of identifying halide ions
to react with any carbonates present to prevent formation of the precipitate Ag2CO3. this would mask the desired observations
2HNO3 + Na2CO3 —> 2NaNO3 + H2O + CO2
what is the colour of the precipitate of the different halide ions
fluorides produce no precipitate
chlorides produce a white precipitate
Ag+(aq) + Cl-(aq) —> AgCl(s)
bromides produce a cream precipitate
Ag+(aq) + Br-(aq) —> AgBr(s)
iodides produce a pale yellow precipitate
Ag+(aq) + I-(aq) —> AgI(s)
what is the effect of ammonia on silver halides
the silver halide precipitates can be
treated with ammonia solution to help differentiate between them if the
colours look similar
what does silver chloride dissolve in
dissolves in dilute ammonia to form a
complex ion
AgCl(s) + 2NH3
(aq) [Ag(NH3)2]+
(aq) + Cl- (aq)
complex ion=colourless solution
what does silver bromine dissolve in
dissolves in concentrated ammonia to form a
complex ion
AgBr(s) + 2NH3(aq) [Ag(NH3)2]+(aq) + Br -(aq)
complex ions =colourless solution
what does silver iodide dissolve in
does not react with ammonia – it is too insoluble
how are hydrogen halides produced and what is the observation
made by the reaction of solid
sodium halide salts with phosphoric acid
NaCl(s) + H3PO4(l) NaH2PO4(s) + HCl(g)
Observations: White steamy fumes of the hydrogen
halides are evolved.
the steamy fumes of HCl are produced when the HCl
meets the air because it dissolves in the moisture in the air
what is the test for carbonate and hydrogencarbonate ions
add any dilute acid and observe effervescence. bubble gas through limewater to test for CO2 – will turn limewater cloudy.
fizzing due to CO2 would be observed if a carbonate or a
hydrogencarbonate was present
what is the test for presence of a sulfate
acidified BaCl2 solution is used as a reagent to test for sulfate ions. if barium chloride is added to a solution that contains sulfate ions a
white precipitate forms
Ba2+(aq) + SO42-(aq) —> BaSO4(s)
what is the test for cations
test for ammonium ion NH4+, by reaction with warm
NaOH(aq) forming NH3
NH4+ +OH- —> NH3 + H2O
what is the test for ammonia gas
ammonia gas can be identified by its
pungent smell or by turning damp red
litmus paper blue
solubility in water of halogen halide
the hydrogen halides are all soluble in water. they dissolve to form acidic solutions
HCl(g)+ H2O(l) —> H3O+(aq)+ Cl-(aq)
what happens when hydrogen halides react with ammonia
the white smoke of the ammonium halide
HCl(g) + NH3(g) —> NH4Cl (s)
HBr(g) + NH3(g) —> NH4Br (s)
HI(g) + NH3(g) —> NH4I(s)
this can be used as a test for the presence of hydrogen halides
