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A Level Chemistry > 5.3 Transition elements > Flashcards

5.3 Transition elements Flashcards

1
Q

d block elements

A

located between group 2 and group 13 of the periodic table

the 3d sub shell has the highest energy and electrons added to 3d orbitals

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2
Q

d block element properties

A

metallic, displaying the typical physical properties of metals
high MP and BPs
shiny in appearance
conduct both electricity and heat

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3
Q

electron configuration of d block elements

A

the electron configuration of an atom or ion shows the arrangement of electrons in shells and sub shells
elecs occupy orbitals in order of increasing energy
electrons fill 4s sub shell before 3d
exceptions- chromium and copper

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4
Q

special case of chromium and copper

A

chromium 1s2 2s2 2p6 3s2 3p6 3d5 4s1
copper 1s2 2s2 2p6 3s2 3p6 3d10 4s1
a half filled d5 sub shell and a fully filled d10 sub shell give additional stability to atoms of chromium and copper

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5
Q

electron configuration of d block ions

A

when 3d block elements form positive ions from their atoms, they lose their 4s elecs before losing any of their 3d elecs. this means that:

  • when forming an atom, the 4s orbital fills before the 3d orbitals
  • when forming an ion, the 4s orbital empties before the 3d orbitals
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6
Q

transition elements

A

d block elements that form at least one ion with a partially filled d orbital
although scandium and zinc are d block elements, they do not match this definition and are not classified as transition elements

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7
Q

why isn’t scandium a transition metal

A

Sc only forms the ion Sc3+ by the loss of two 4s elecs and one 3d elec
-the elec config of Sc 1s2 2s2 2p6 3s2 3p6 3d1 4s2
-Sc3+ has an elec config of 1s2 2s2 2p6 3s2 3p6
Sc3+ ions have empty 3d orbitals
so Sc doesn’t form ions with partially filled d orbitals and are therefore not classified as transition metals

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8
Q

why isn’t zinc a transition metal

A

zinc only forms the Zn2+ ion by the loss of its two 4s elecs
-the elec config of Zn is 1s2 2s2 2p6 3s2 3p6 3d10 4s2
-Zn2+ has the elec config of 1s2 2s2 2p6 3s2 3p6 3d10
Zn2+ ions have full d orbitals
so zinc doesn’t form ions with partially filled d orbitals and are therefore not classified as transition metals

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9
Q

properties of transition metals and their compounds

A
  • they form compounds in which the transition element has diff oxidation states
  • they form coloured compounds
  • the elements and their compounds can act as catalysts
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10
Q

transition element’s variable oxidation states

A

they form compounds with more than one oxidation state
e.g. iron forms two chlorides- iron (ii) chloride, FeCl2, and iron (iii) chloride, FeCl3
the number of oxidation states increases across the transition elements series to manganese, and then decreases

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11
Q

transition elements- formation of coloured compounds

A

compounds and ions of TE are frequently coloured
the solid compounds can be dissolved in water to produce coloured solutions
the colour of a solution is linked to the partially filled d orbitals of the transition metal ion
the colour of a solution can vary with different oxidation states

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12
Q

transition metals as catalysts

A

Cu2+ is used as a catalyst for the reaction of Zn with acids

MnO2 is used as a catalyst for decomposition of H2O2

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13
Q

colours of iron in oxidation state +2 and +3

A

+2 is pale green

+3 is yellow

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14
Q

colours of chromium in oxidation state as Cr2O7^2-, +6 and as Cr^3+, +3

A

+6 is yellow/orange

+3 is green

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15
Q

complex ion

A

a transition metal ion bonded to ligands by coordinate bonds (dative covalent bonds)

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16
Q

ligand

A

a molecule or ion that donates a pair of electrons to a central metal ion to form a coordinate bond

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17
Q

coordinate/dative covalent bond

A

a special kind of covalent bond is formed when one of the bonded atoms provides both of the elecs for the shared pair

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18
Q

coordination number

A

indicates the number of coordinate bonds attached to the central metal ion

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19
Q

representing complex ions

A

in its formula, the complex ion is enclosed inside square brackets with the overall charge of the complex shown outside of the square brackets
the overall charge on a complex ion is the sum of the charges on the central metal ion and any ligands present
e.g. [Cr(H2O)6]3+

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20
Q

monodentate ligands

A

a ligand that is able to donate one pair of elecs to a central metal ion
e.g. water, ammonia, chloride, cyanide and hydroxide

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21
Q

bidentate ligands

A

ligands that can donate two lone pairs of elecs to the central metal ion, forming two coordinate bonds
e.g. 1,2-diaminoethane (frequently shortened to en) NH2CH2CH2NH2

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22
Q

1,2-diaminoethane

A

each nitrogen atom donates a pair of electrons to the central metal ion forming a coordinate bond

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23
Q

shapes of complex ions

A

depends upon its coordination number

most common coordination numbers are six and four giving rise to six-coordinate and four-coordinate complexes

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24
Q

six-coordinate complexes

A

many complex ions have a coordination number of six, giving an octahedral shape
e.g. [Mn(H2O)6]2+ and [Co(H2NCH2CH2NH2)3]3+

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25
Q

four coordinate complexes

A

complexes with a coordination number of four have two common shapes- tetrahedral and square planar

26
Q

tetrahedral complexes

A

four-coordinate complexes

e.g. [CoCl4]2- and [CuCl4]2-

27
Q

square planar complexes

A

four-coordinate complexes
occurs in complex ions with eight d-electrons in the highest energy d-sub-shell
Platinum (II), Palladium (II) and gold (III) fall in this category and tend to form square planar complexes
e.g. [Pt(NH3)4]2+

28
Q

stereoisomerism in complex ions

A

for complex ions, the stereoisomerism depends on the number and type of ligands that are attached to the central metal ion, and the shape of the complex

29
Q

cis-trans isomerism in complex ions

A

cis-trans isomerism stereoisomerism requires the presence of a C=C double bond which prevents rotation of groups attached to each carbon atom of the C=C bond
in complex ions, no double bond is involved and the shape of the complex holds groups in different orientations about the central metal ion
cis-trans isomerism occurs in some square planar and octahedral complex ions

30
Q

cis-trans isomerism in square planar complexes

A

in square planar complexes the ligands are arranged in the same plane at the corners of a square with 90 degree bond angles
in the cis-isomer, the two identical groups are adjacent to each other
in the trans-isomer, the two identical groups are opposite each other

31
Q

cis-trans isomerism in octahedral complexes- monodentate ligands

A

in the cis-isomer, two identical groups are adjacent to each other
in the trans-isomer, two identical groups are at opposite corners of the octahedron

32
Q

optical isomerism in octahedral complexes

A

optical isomerism only occurs in octahedral complexes containing two or more bidentate ligands
optical isomers, called enantiomers, are non-superimposable mirror images of each other

33
Q

role of cis-trans isomerism in medicine

A

cis-platin
attacks tumours and in many cases the tumours were seen to shrink in size
used extensively in the treatment of cancer
it works by forming a platinum complex inside of a cell which binds to dna and prevents the dna of the cell from replicating

34
Q

ligand substitution reactions

A

reactions where one ligand in a complex ion is replaced by another ligand

35
Q

reactions of aqueous copper (II) ions

A

when copper (II) sulfate is dissolved in water, the pale blue complex ion, [Cu(H2O)6]2+ is formed in aqueous solution

36
Q

reactions of aqueous copper (II) ions- ligand substitution with ammonia

A

[Cu(H2O)6]2+(aq) + 4NH3(aq) –> [Cu(NH3)4(H2O)2]2+(aq) + 4H2O(l)
pale blue solution –> dark blue solution
4 ammonia ligands have replaced 4 of the water ligands
both are octahedral complex ions
ammonia should be added dropwise so you can observe the two different reactions taking place:
-a pale blue precip of Cu(OH)2 is formed in the first stage of the reaction
-the Cu(OH)2 precip then dissolves in excess ammonia to form a dark blue solution

37
Q

reactions of aqueous copper (II) ions- ligand substitution with chloride ions

A

[Cu(H2O)6]2+(aq) + 4Cl-(aq) <=> [CuCl4]2-(aq) + 6H2O(l)
pale blue solution <=> yellow solution
octahedral <=> tetrahedral

38
Q

reactions of aqueous chromium (III) ions

A

when chromium (III) potassium sulfate, KCr(SO4)2·12H2O, is dissolved in water, the complex ion [Cr(H2O)6]3+ is formed
this is a pale purple solution
when chromium (III) sulfate is dissolved in water, a green solution containing chromium (III) is formed
however this solution is not [Cr(H2O)6]3+, rather it is the complex ion [Cr(H2O)5SO4]+, where one of the water ligands has been replaced by the sulfate ion, SO4^2-

39
Q

reactions of aqueous chromium (III) ions- reaction with ammonia

A

[Cr(H2O)6]3+(aq) + 6NH3(aq) –> [Cr(NH3)6]3+(aq) + 6H2O(l)
violet –> purple
when the ammonia is added drop-wise, the reaction takes place in two steps:
-initially a grey-green precip of Cr(OH)3 is formed
-the Cr(OH)3 precip dissolves in excess ammonia to form the complex ion [Cr(NH3)6]3+ (purple)

40
Q

ligand substitution and haemoglobin

A

carbon monoxide can also bind to the Fe2+ ion in haemoglobin
forms the complex carboxyhaemoglobin
if CO is inhaled, a ligand substitution reaction takes place where the O2 in haemoglobin is replaced by CO
CO binds to H more strongly than O2, so a small conc of CO in the lungs can prevent a large proportion of the H molecules from carrying O2
the bond is so strong that this process is irreversible
if the conc of carboxyhaemoglobin is too high, O2 transport is prevented, leading to death

41
Q

haemoglobin

A

blood carries O2 around the body due to the presence of haemoglobin, the iron-containing protein present in all red blood cells
haemoglobin contains four protein chains held together by weak intermolecular forces
each protein chain has a haem molecule within its structure
the central metal ion in a haem group is Fe2+ which can bind to oxygen gas

42
Q

haemoglobin function

A

as blood passes through the lungs, the haemoglobin bonds to O2 because of the inc oxygen pressure in the capillaries of the lungs
oxyhaemoglobin is formed, which releases this O2 to body cells as and when required
the haemoglobin can also bond to CO2, which is carried back to the lungs

43
Q

precipitation reaction

A

occurs when two aqueous solutions containing ions react together to form an insoluble ionic solid, called a precipitate

44
Q

precipitation reactions with sodium hydroxide- Cu2+

A

blue solution reacts to form a blue precip of copper (II) hydroxide
the precip is insoluble in excess NaOH

Cu2+(aq) + 2OH-(aq) –> Cu(OH)2(s)
blue precip

45
Q

precipitation reactions with sodium hydroxide- Fe2+

A

pale green solution reacts to form a green precip of iron (II) hydroxide
the precip is insoluble in excess NaOH but turns brown at its surface on standing in air as iron (II) is oxidised to iron (III)

Fe2+(aq) + 2OH-(aq) –> Fe(OH)2(s)
green precip
in air: Fe(OH)2 –> Fe(OH)3(s)
orange-brown precip

46
Q

precipitation reactions with sodium hydroxide- Fe3+

A

pale yellow solution reacts to form an orange-brown precip of Iron (III) hydroxide
the precip is insoluble in excess NaOH

Fe3+(aq) + 3OH-(aq) –> Fe(OH)3(s)
orange-brown precip

47
Q

precipitation reactions with sodium hydroxide- Mn2+

A

pale pink solution reacts to form a light brown precip of manganese (II) hydroxide which darkens on standing in air
the precip is insoluble in excess NaOH

Mn2+(aq) + 2OH-(aq) –> Mn(OH)2(s)
light-brown precip

48
Q

precipitation reactions with sodium hydroxide- Cr3+

A

violet solution reacts to form a grey-green precip of chromium (III) hydroxide
the precip is soluble in excess NaOH forming a dark green solution

Cr3+(aq) + 3OH-(aq) –> Cr(OH)3(s)
green precip
Cr(OH)3(s) + 3OH-(aq) –> [Cr(OH)6]3-(aq)

49
Q

precipitation reactions with ammonia- Cu2+

A

the blue precip Cu(OH)2(s) dissolves in excess ammonia to form a deep blue solution with the formula [Cu(NH3)4(H2O)2]2+(aq)

50
Q

precipitation reactions with ammonia- Cr3+

A

the green precip Cr(OH)3(s) dissolves in excess ammonia to form [Cr(NH3)6]3+(aq) which is a purple solution

51
Q

precipitation reactions with ammonia

A

only Cu2+ and Cr3+ react

Fe2+, Fe3+ and Mn2+ precipitates have no further reaction with aqueous ammonia so the precips don’t dissolve

52
Q

oxidation of Fe2+ to Fe3+

A

Fe2+ can be oxidised with H+/MnO4^-
solution containing MnO4^- ions is purple and is decolourised by Fe2+ ions to form a colourless solution containing Mn2+ ions

53
Q

reduction of Fe3+ to Fe2+

A

Fe3+ can be reduced with I-
the orange-brown Fe3+ ions are reduced to pale green Fe2+ ions
this colour change is obscured by the oxidation of iodide ions o form iodine which has a brown colour

54
Q

reduction of Cr2O7^2- to Cr3+

A

Cr2O7^2- reduced with Zn/H+
orange to green
with excess zinc, Cr3+ is reduced further to Cr2+, pale blue

55
Q

oxidation of Cr3+ to CrO4^2-

A

Cr3+ can be oxidised with H2O2/OH– (hot alkaline hydrogen peroxide)
green to yellow

56
Q

reduction of Cu2+ to Cu+

A

Cu2+ can be reduced with iodide ions, I-
the Cu+ forms a white precip of copper (I) iodide
iodine also formed- brown

57
Q

disproportionation of Cu+ ions

A

when solid copper (I) oxide, Cu2O, reacts with hot dilute sulfuric acid, a brown precip of copper is formed together with a blue solution of copper (II) sulfate
in this reaction, the Cu+ ions have been simultaneously oxidised and reduced

58
Q

identifying transition metal ions - qualitative analysis

A

aqueous sodium hydroxide produces precips with aqueous transition metal ions

59
Q

identifying ammonium ions - qualitative analysis

A

when heated with hydroxide ions, NH4^+ reacts to produce ammonia gas, NH3
NaOH and heat
damp litmus paper- turn blue

60
Q

identifying carbonate ions - qualitative analysis

A

add dilute nitric acid

effervescence as CO2 is evolved

61
Q

identifying sulfate ions - qualitative analysis

A

add Ba2+(aq) ions

white precip of BaSO4 formed

62
Q

identifying halide ions - qualitative analysis

A

add Ag+(aq) ions

  • white precip of AgCl is Cl- ions present, soluble in dilute NH3(aq)
  • cream precip of AgBr if Br- ions present, soluble in conc NH3(aq)
  • yellow precip of AgI if I- ions present, insoluble in NH3

A Level Chemistry (16 decks)

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