transition metals Flashcards
where are transition metals found
d block
what are transition metals
d block elements that can form one or more stable ions with incompletely filled d orbitals
what d block elements are not transition metals
scandium and zinc
why isn’t scandium a transition metal
scandium only forms one ion Sc³⁺ which has a empty d sub shell
it has configuration [Ar]3d¹4s² when it loses three electrons it has configuration of [Ar]
why isnt zinc a transition metal
zinc only forms Zn²⁺ which has a full d sub shell
its configuration is [Ar] 3d¹⁰4s² when it loses two electrons it has a full 3d subshell
transition metals have variable … numbers
oxidation
transition metals can have variable oxidation numbers because they form multiple …
stable ions
what needs to happen to form a compound or a complex containing an ion with a certain oxidation number
energy given out when complex is formed has to be bigger than the energy taken to remove outer electrons and form the ion (the ionisation energy)
transition metals form ions from losing electrons from which subshells
4s and 3d
why does it take similar amounts of energy to remove an electron from 4s sub shell and the 3d sub shell
because the 4s sub shell and the 3d sub shell have similar energy levels
what happens to the energy released when ions form complexes with increasing ionic charge
increases
what is a complex ion
metal ion surrounded by dative covalently (coordinately) bonded ligands
what is a ligand
a atom ion or molecule that donates a pair of electrons to a central metal atom or ion
what must a ligand have
at least one lone pair of electrons or it wont have anything to form a dative covalent bond with
ligands with one lone pair are called
monodentate
eg. H₂O: :NH₃ :Cl ⁻ :OH⁻
ligands with two lone pairs are called
bidentate
example of bidentate ligand
1,2-diaminoethane
NH₂CH₂CH₂NH₂
which ligands can form two dative covalent bonds with a metal ion
bidentate ligands
ligands with more than two lone pairs are called
multidentate
EDTA⁴⁻ has six lone pairs what ligand is it and how many dative covalent bonds can it form
hexadentate ligand/multidentate
and can form six dative covalent bonds with metal ion
what does haemoglobin do
transport oxygen around the body
what metal complex is haemoglobin
iron(II)
what type of ligand is haemoglobin
a multidentate ligand called a haem group
what is a haem group made up of
a ring containing 4 nitrogen atoms with iron at the centre
the overall charge on a complex ion is its
oxidation number
where would you put the charge on a complex ion
outside the square brackets
oxidation number of the metal ion =
total oxidation number - sum of the charges of the ligand
work out the charge of the metal ion iron in [Fe(CN)6]⁴⁻
total oxidation number = -4
CN⁻ ligand charge = -1
iron oxidation number = -4 - (6 x -1 ) = +2
what is the coordination number
number of dative covalent (coordinate) bonds formed with central metal ion
what are usual coordinate numbers
6 and 4
if a ligand is small what is the usual coordinate number
6
if a ligand is larger what is the usual coordinate number
4
why are the ligands positioned as far away from each other
because bonding electrons in dative covalent bond of a complex repel each other
what is the shape and bond angle in six fold coordination
octahedral shape and all bond angles are 90
what is th shape and bond angle in four fold coordination
tetrahedral shape bong angles are 109.5
what is the other occasional four fold coordination
square planar where bond angles are 90
eg cis-platin
cis/trans isomerism a form of
E/Z isomerism
which shape complex ions can show cis/trans isomerism
square planar and octahedral
what happens to the groups in cis isomers
they are on the same side
what happens tot he groups in trans isomers
same groups opposite each other
what metal complex is cis-platin
platinum(II)
what ligands are on cis-platin
two chloride ions and two ammonia molecules
what shape is cis-platin
square planar and so has bond angles of 90
what is cis-platin used for
anti cancer drug
why cant trans-platin be given to patients being treated for cancer
its toxic
what happens to 3d orbital when ligands bond to the central ion
3d orbital splits into two different energy levels
what orbitals do electrons tend to occupy
the lower orbitals
what do electrons need to jump up to higher electron orbitals
energy equal to the energy gap
where do electrons get the energy to jump up to higher orbitals
from visible light
for larger energy gaps does the frequency of light absorbed increase or decrease
increase
what affects the size of the energy gap
central metal ion
the central metal ions oxidation number
the ligands
coordination number
what happens to the rest of the frequencies of light that are not absorbed
they are transmitted or reflected
what do the transmitted or reflected frequencies of light do
combine to make the complement of the colour of the absorbed frequencies
from red to purple light what happens to the frequency
frequency increases
what is the complimentary of red
cyan
what is the complementary of yellow
blue
what is the complementary of green
magenta
what is the complementary of cyan
red
what is the complementary of blue
yellow
what is the complementary of magenta
green
if there are no 3d electrons what does this mean in terms of energy
no energy can be absorbed
if no energy can be absorbed what colour will the compound be
white or colourless
when solid containing transition metal ion is dissolved in water what happens
transition metal will form aqueous complex in solution
what happens in a aqueous water complex
metal ion is surrounded by water ligands
what can the colour of the aqueous solutions do
help us identify transition metal that is present
what colour is Mn+7/MnO₄⁻
purple
what colour is chromium+6/Cr₂O₇²⁻
orange
what colour is magnese+6/MnO₄²⁻
green
what colour is vanadium+5/VO₂⁺
yellow
what colour is vandium+4/VO²⁺
blue
what colour is titanium+3/Ti³⁺
purple
what colour is vanadium+3/V³⁺
green
what colour is chromium+3/Cr³⁺
green
what colour is iron+3/Fe³⁺
yellow
what colour is titanium+2/Ti²⁺
violet
what colour is vanadium+2/V²⁺
violet
what is the colour of magnese+2/Mn²⁺
pale pink
what is the colour of iron+2/Fe²⁺
pale green
what colour is cobalt+2/Co²⁺
pink
what colour is nickel+2/Ni²⁺
green
what colour is copper+2/Cu²⁺
pale blue
how many oxidation numbers can vanadium exist in in solution
four
each reduction reaction has its own
reducing potential
reduction potentials are another name for
electrode potentials
reduction potentials allow you to work out if
redox reactions involving transition metals are likely to happen
what ion does chromium form with oxygen
chromate(VI) ions [CrO₄²⁻]
dichromate(VI) ions [Cr₂O₇²⁻]
why are chromate(VI) ions [CrO₄²⁻], dichromate(VI) ions [Cr₂O₇²⁻] good oxidising agents
because they are easily reduced to Cr³⁺
what colour are Cr³⁺ ions when surrounded by 6 water ligands
violet
why will Cr³⁺ ions in solution sometimes look green
because the water ligands can be substituted with impurities eg Cl⁻
write the reaction of of dichromate (VI) ions/Cr₂O₇²⁻ with zinc and dilute acid
Cr₂O₇²⁻(aq) + 14H⁺(aq) + 3Zn(s) ⟶ 3Zn²⁺(aq) + 2Cr³⁺(aq) + 7H₂O(l)
write the second reaction of zinc reducing Cr³⁺
2Cr³⁺(aq) + Zn(s) ⟶ Zn²⁺(aq) + 2Cr²⁺(aq)
why do you need to use inert atmosphere when reacting zinc with Cr³⁺
Cr²⁺ is so unstable that it oxidises straight back to Cr³⁺ in air
reaction of Cr³⁺ with hydrogen per oxide in alkaline solution
2Cr³⁺(aq) + 10OH⁻(aq) + 3H₂O₂(aq) ⟶ 2CrO₄²⁻(aq) + 8H₂O(l)
reaction of 2CrO₄²⁻ with acid
2CrO₄²⁻(aq) + 2H⁺(aq) ⇌ Cr₂O₇²⁻(aq) + H₂O(l)
what happens when you mix aqueous solution of chromium(II) ions with aqueous sodium hydroxide or aqueous ammonia
you get chromium hydroxide precipitate
[Cr(H2O)6]³⁺(aq) + 3OH⁻(aq)⟶
Cr(OH)3(H₂O)₃ + 3H₂O(l)
[Cr(H₂O)₆]³⁺(aq) + 3NH₃(aq)⟶
Cr(OH)₃(H₂O)₃ + 3NH₄⁺(aq)
what colour is chromium hydroxide precipitate/[Cr(OH)₃(H₂O)₃]
a grey green precipitate
what does amphoteric mean
can react as a acid or base
chromium hydroxide is amphoteric so
it reacts with both acids and bases
chromium hydroxide reacts with both acids and bases so its
amphoteric
[Cr(OH)₃(H₂O)₃] +3H⁺⟶
[Cr(H₂O)₆]³⁺
[Cr(OH)₃(H₂O)₃] + 3OH⁻⟶
[Cr(OH)₆]³⁻ + 3H₂O
if you add excess sodium hydroxide to chromium hydroxide precipitate the H₂O ligands
depropanate
If you add acid to the chromium hydroxide precipitate, the OH⁻ ligands
protonate
if you add excess NH₃ to chromium hydroxide precipitate
a ligand exchange reaction occurs
Cr(OH)₃(H₂O)₃ + 6NH₃(aq)⟶
[Cr(NH₃)₆]³⁺(aq) + 3OH⁻(aq) + 3H₂O(l)
what is the first steps in making chromium (II) ethanoate
*orange sodium dichromate is reduced with zinc in acid solution to form green solution
*Cr₂O₇²⁻(aq) + 14H⁺(aq) +3Zn(s)⟶3Zn²⁺(aq) + 2Cr³⁺(aq) +7H₂O(l)
*and then give blue solution of Cr²⁺ ions
*2Cr³⁺(aq) + Zn(s) ⟶ 2Cr²⁺(aq) + Zn²⁺(aq)
what is the second step in making chromium (II) ethanoate
*sodium ethanoate mixed with solution and red precipitate of chromium (II) ethanoate
*2Cr²⁺(aq) + 4CH₃COO⁻(aq) + 2H₂O(l) ⟶ Cr₂(CH₃COO)₄(H₂O)₂
Cr²⁺ are very easily oxidised what should you do to stop them being oxidised
*do experiment in inert atmosphere eg nitrogen
*remove air and all oxygen from all the liquids by bubbling nitrogen through them
when ligands are swapped and are of the same size what happens to coordination number and the shape of the complex
coordination number does not change and neither does the shape
if a small uncharged ligand is substituted for large charged ligand what happens to coordination number and change of shape
there’s a change of shape and coordination number
[Cr(H₂O)₆]³⁺(aq) + 6NH₃(aq) ⇌
and what is the colour change
[Cr(NH₃)₆]³⁺(aq) + 6H₂O(l)
*dark green to purple
[Cu(H₂O)₆]²⁺(aq) + 4Cl⁻(aq) ⇌
and what is the colour change
[CuCl₄]²⁻(aq) + 6H₂O(l)
*pale blue to yellow
[Co(H₂O)₆]²⁺(aq) + 4Cl⁻(aq) ⇌
and what is the colour change
[CoCl₄]²⁻(aq) + 6H₂O(l)
pale pink to blue
[Cu(H₂O)₆]²⁺(aq) + 4NH₃(aq) ⇌
and what is the colour change
[Cu(NH₃)₄(H₂O)₂]²⁺(aq) + 4H₂O(l)
pale blue to deep blue
how is carboxyhemoglobin formed
oxygen or water molecule in haemoglobin is replaced in ligand exchange reaction with carbon monoxide
why does carbon monoxide poisoning happen
because carbon monoxide forms strong dative covalent bonds with iron and doesn’t readily exchange with oxygen or water ligands meaning haemoglobin can’t transport oxygen
more stable complexes have a positive or negative entropy change
positive
why do ligand exchange reactions have small enthalpy change reactions
dative bonds are broken and formed strength of bonds broken is similar to the strength of the new bonds so enthalpy change is usually small
why does entropy increase when mono dentate ligands substituted with bi dentate ligands or multi dentate ligands
because when they are substituted the number of particles in solution increases the more particles the greater the entropy reactions with increase in entropy are more likely to happen
which reaction is more likely to happen a reaction with a increase in entropy or a reaction with a decrease in entropy
the reaction with a increase In entropy
when EDTA⁴⁻ replaces mono dentate ligand why does the complex become more stable
because the number of particles in solution increases, the more particles the greater the entropy, the greater the entropy the more stable the complex formed
what characteristic do transition element hydroxides have
brightly coloured precipitates
what happens when you mix aqueous solution of transition element ions with aqueous sodium hydroxide and or aqueous ammonia
water ligands are deprotonated in acid base reaction and you get a coloured hydroxide precipitate
how can you reverse transition element ions with aqueous sodium hydroxide or aqueous ammonia
adding an acid to hydroxide percipitate as the hydroxide ligands will protonate and precipitate will dissolve as soluble meta aqua ions
[Cu(H₂O)₆]²⁺(aq) + 2OH⁻(aq)⟶
and what is the colour change
Cu(OH)₂(H₂O)₄](s) + 2H₂O(l)
pale blue solution to blue precipitate
[Cu(H₂O)₆]²⁺(aq) + 2NH₃(aq)⟶
and what is the colour change
Cu(NH₃)₂(H₂O)₄ + 2NH₄⁺(l)
pale blue solution to blue precipitate
Cu(OH)₂(H₂O)₄ + 4NH₃(aq) ⟶ [Cu(NH₃)₄(H₂O)₂]²⁺(aq) + 2OH⁻(aq) + 4H₂O(l)
is what type of reaction
ligand exchange reaction
Cu(OH)₂(H₂O)₄ + 4NH₃(aq) ⟶
and what is the colour change
[Cu(NH₃)₄(H₂O)₂]²⁺(aq) + 2OH⁻(aq) + 4H₂O(l)
blue precipitate to deep blue solution
[Fe(H₂O)₆]²⁺(aq) + 2OH⁻(aq) ⟶
and what is the colour change
Fe(OH)₂(H₂O)₄ + 2H₂O(l)
pale green solution to green precipitate
[Fe(H₂O)₆]²⁺(aq) + 2NH₃(aq) ⟶
and what is the colour change
Fe(OH)₂(H₂O)₄ + 2NH₄⁺(aq)
pale green solution to green precipitate
[Fe(H₂O)₆]³⁺(aq) + 3OH-(aq) ⟶
and what is the colour change
Fe(OH)₃(H₂O)₃ + 3H₂O(aq)
yellow solution to an orange precipitate
[Fe(H₂O)₆]³⁺(aq) + 3NH₃(aq) ⟶
and what is the colour change
Fe(OH)₃(H₂O)₃ + 3NH₄⁺(aq)
yellow solution to orange precipitate
[Co(H₂O)₆]²⁺(aq) + 2OH⁻(aq) ⟶
and what is the colour change
Co(OH)₂(H₂O)₄ + 2H₂O(l)
pale pink solution to a blue precipitate which turns brown on standing
[Co(H₂O)₆]²⁺(aq) + 2NH₃(aq) ⟶
and what is the colour change
Co(OH)₂(H₂O)₄ + 2NH₄⁺(aq)
pale pink solution to a blue precipitate which turns brown on standing
Co(OH)₂(H₂O)₄ + 6NH₃(aq) ⟶ [Co(NH₃)₆]²⁺(aq) + 2OH⁻(aq) + 4H₂O(l)
is a
ligand exchange reaction
Co(OH)₂(H₂O)₄ + 6NH₃(aq) ⟶
what’s the colour change
[Co(NH₃)₆]²⁺(aq) + 2OH⁻(aq) + 4H₂O(l)
the blue precipitate dissolves to form yellow brown solution
why do transition metals make good catalyst
because they can change oxidation number by gaining or losing electrons within their d orbitals this means they can transfer electrons to speed up reactions
V₂O₅ + SO₂ ⟶ V₂O₄ + SO₃
V₂O₄ + ½O₂ ⟶ V₂O₅
what is happening here
*vanadium oxidises SO₂ to SO₃ and is reduced itself
*the reduced catalyst is oxidised by oxygen gas back to its original state
*catalyst ready to do process all over again
what are homogenous catalyst
catalyst in the same state as the the reactants
what state is a homogenous catalyst usually
an aqueous catalyst for a reaction between two aqueous solutions
how do homogenous catalyst work
work by combining with the reactants to form intermediate species and then react to form products and reform the catalyst
what is true about the energy needed to form the intermediate species which then reacts to form the products and reform the catalyst
the energy needed to form the intermediate is lower than that needed to make the product directly from reactants
why is the catalyst always able to catalyse the reaction
because its always reformed
why is the reaction between iodide ions and peroxodisulfate (S₂O₈²⁻) really slow
because the ions are both negatively charged so they repel each other so its unlikely they’ll collide and react
why doe the reaction between peroxodisulfate (S₂O₈²⁻) ad iodide ions become faster when you add Fe²⁺ ions
because each stage involves a positive and negative ions so there’s no repulsion
write the reactions between peroxodisulfate (S₂O₈²⁻) ad iodide ions when you add Fe²⁺ ions
*S₂O₈²⁻(aq) + 2Fe²⁺(aq) ⟶ 2Fe³⁺(aq) + 2SO₄²⁻(aq)
*2Fe³⁺(aq) + 2I⁻(aq) ⟶I₂(aq) + 2Fe²⁺(aq)
*S₂O₈²⁻(aq) + 2Fe²⁺(aq) ⟶ 2Fe³⁺(aq) + 2SO₄²⁻(aq)
*2Fe³⁺(aq) + 2I⁻(aq) ⟶I₂(aq) + 2Fe²⁺(aq)
explain what’s going on
*first the Fe²⁺ ions are oxidised to Fe³⁺ ions by S₂O₈²⁻
*the newly formed intermediate Fe³⁺ ions now easily oxidise the I⁻ ions to iodine and the catalyst is regenerated
what is autocatalysis
Autocatalysis the term used to describe a reaction which is speeded up by a product which acts as a catalyst for the reaction
how can you reduce Cr₂O₇²⁻ to Cr³⁺ and Cr²⁺
using zinc in acidic conditions
