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chemistry module 5 > transition elements > Flashcards

transition elements Flashcards

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1
Q

what type of element are the transition elements

A

metals - meaning they all have metallic properties

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2
Q

transition element definition

A

d-block elements that form at least 1 ion with a partially filled d orbital

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3
Q

what are the 2 d-block elements that are not classified as transition elements

A

Sc and Zn
these elements only form Sc3+ and Zn2+ which empties/fills d sub shells
they are just d-block elements

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4
Q

which 2 transition elements have exceptional electron configurations

A

Cr and Cu
their configurations should end in 3d4 4s2 and 3d9 4s2 respectively, but 3d4 and 3d9 are very unstable as they are so close to 3d5 and 3d10, which are much more stable arrangements
so their electron configurations become 3d5 4s1 and 3d10 4s1
- both still transition metals !

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5
Q

4 properties of transition elements + examples

A
  • multiple oxidation states
  • they form coloured compounds
  • the elements and their compounds can act as catalysts
  • they can form complex ions

e.g. iron (ii) which is pale green and iron (iii) which is brown-yellow, iron is a catalyst for the haber process

remember they also have the same properties as normal metals

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6
Q

complex ion definition

A

a central metal ion with 1 or more molecules or charged ions bound to it by dative covalent bonds
usually formed by d-block elements - not all of them e.g. not Zn - but can also be formed by other elements e.g. Al

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7
Q

ligand definition

A

a molecule/atom/ion that donates a pair of electrons to a central metal atom by dative covalent bonding - it must have a lone pair

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8
Q

what are the 2 types of ligands + examples for each

A

neutral e.g. H2O, NH3
charged e.g. CN- , OH-, halide ions

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9
Q

coordinate number definition

A

the number of dative bonds made to the central metal ion
- not = to number of ligands

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10
Q

monodentate ligand definition

A

a molecule/atom/ion which can form 1 dative bond by donating 1 lone pair

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11
Q

bidentate ligand definition

A

a molecule/atom/ion which can form 2 dative bonds by donating 2 lone pairs

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12
Q

polydentate ligand definition

A

a molecule/atom/ion which can form more than 2 dative bonds by donating more than 2 lone pair

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13
Q

what shape would a complex ion with a coordinate number of 6 be

A

octahedral

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14
Q

what shapes could a complex ion with a coordinate number of 4 be

A

tetrahedral
square planar

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15
Q

what is the bond angle in a square planar

A

90°

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16
Q

what type of complex is [x(H2O)6]

A

… hexaaqua

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17
Q

what shape are hexaaqua complexes normally

A

octahedral

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18
Q

what type of complex is [xCl4]

A

… tetrachloro

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19
Q

what shape are tetrachloro complexes normally

A

tetrahedral

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20
Q

what type of transition elements tend to form square planars + 3 examples

A

transition metals with 8d electrons
e.g. platinum (II), gold (III)

21
Q

give 2 examples of bidentate ligands

A

1,2 - diaminoethane
H2N-CH2-CH2-NH2

ethandioate (a dicarboxylate ion)
-OOC-COO-

22
Q

optical isomerism definition

A

molecules with the same molecular formula but are nonsuperimposable mirror images of each other

23
Q

what 3 types of complex ions can display cis-trans isomerism

A
  • square planar complexes with 2 identical ligands (not more) - cis=adjacent, trans=opposite
  • octahedral complexes with 4 of one ligand and 2 of another - cis=adjacent, trans=opposite
  • octahedral complexes with 2 monodentate and 2 bidentate ligands - cis=adjacent, trans=opposite
24
Q

what type of complex ion can display optical isomerism

A

a complex ion with 2 or more bidentate ligands

25
Q

outline the role of cis-trans isomerism in complex ions in medicine (cis-platin)

A
  • cis-platin is a complex ion with the formula [Pt(NH3)2Cl2]
  • it is able to form a platinum complex inside a cell which binds to DNA, preventing DNA replication and therefore mitosis
  • activation of the cells own repair system then leads to apoptosis
  • it has been used in chemotherapy as it can attack tumours, even causing them to shrink in size
  • there are some unpleasant side effects however, many of which lead to kidney damage
26
Q

what effect does adding NH3 or NaOH have on aq transition metal complexes

A

it causes the formation of coloured precipitates of the insoluble transition metal hydroxides
- this is because they both dissociate in aq solution to form a supply of OH-
- the precipitates can then be redissolved by adding acid

27
Q

ligand exchange/substitution definition

A

a reaction when ligands in a complex ion are swapped for another
- this often causes a colour change

28
Q

what happens to metal complexes in ligand substitution reactions with similarly sizes + uncharged ligands

A

coordinate number and shape will not change

29
Q

what happens to metal complexes in ligand substitution reactions from small uncharged to larger charged ligands or vice versa

A

the coordinate number and shape will change

30
Q

give the formula + colours for Cr3+ as:
- metal-aqua ion
- with OH-
- with excess OH-
- with NH3
- with excess NH3

A

metal-aqua ion
[Cr(H2O)6]3+ - violet solution

with OH-
Cr(OH)3(H2O)3 - grey- green precipitate

with excess OH-
[Cr(OH)6]3- - dark green solution

with NH3
Cr(OH)3(H2O)3 - grey-green precipitate

with excess NH3
[Cr(NH3)6]3+ - purple solution

31
Q

give the formula + colours for Fe2+ as:
- metal-aqua ion
- with OH-
- with excess OH-
- with NH3
- with excess NH3

A

metal-aqua ion
[Fe(H2O)6]2+ - pale green solution

with OH-
Fe(OH)2(H2O)4 - green precipitate, turns brown on the surface over time

with excess OH-
no change - doesn’t react so stays as insoluble precipitate

with NH3
Fe(OH)2(H2O)4 - green precipitate, turns brown on the surface over time

with excess NH3
no change - doesn’t react so stays as insoluble precipitate

32
Q

give the formula + colours for Fe3+ as:
- metal-aqua ion
- with OH-
- with excess OH-
- with NH3
- with excess NH3

A

metal-aqua ion
[Fe(H2O)6]3+ - pale yellow solution

with OH-
Fe(OH)3(H2O)3 - orange-brown precipitate

with excess OH-
no change - doesn’t react so stays as insoluble precipitate

with NH3
Fe(OH)3(H2O)3 - orange-brown precipitate

with excess NH3
no change - doesn’t react so stays as insoluble precipitate

33
Q

give the formula + colours for Mn2+ as:
- metal-aqua ion
- with OH-
- with excess OH-
- with NH3
- with excess NH3

A

metal-aqua ion
[Mn(H2O)6]2+ - pink solution

with OH-
Mn(OH)2(H2O)4 - pale brown precipitate

with excess OH-
no change - doesn’t react so stays as insoluble precipitate

with NH3
Mn(OH)2(H2O)4 - pale brown precipitate

with excess NH3
no change - doesn’t react so stays as insoluble precipitate

34
Q

give the formula + colours for Cu2+ as:
- metal-aqua ion
- with Cl-
- with OH-
- with excess OH-
- with NH3
- with excess NH3

A

metal-aqua ion
[Cu(H2O)6]2+ - blue solution

with Cl-
[CuCl4]2- - yellow solution

with OH-
Cu(OH)2(H2O)4 - blue precipitate

with excess OH-
no change - doesn’t react so stays as insoluble precipitate

with NH3
Cu(OH)2(H2O)4 - blue precipitate

with excess NH3
[Cu(NH3)4(H2O)2]2+ - dark blue precipitate
- only a partial substitution occurs here

35
Q

why are metal-aqua ions the same colour as the lone transition metal ion

A

this is because H2O is an uncharged ligand, meaning that the oxidation state is the same as its lone ion, so the colour is the same

36
Q

why is there sometimes a colour change between reacting a transition metal ion with NH3 and excess NH3

A

this is because the NH3 doesn’t get substituted unless it’s in excess, it just provides a source of OH-
- the reaction with OH- changes the oxidation state so there is usually a colour change

when the NH3 does get substituted, as NH3 is an uncharged ligand, the oxidation state reverts back to its normal oxidation state, causing a colour change, although it doesn’t change back to the same colour it is as a lone ion
- this doesn’t occur for all transition metal ions, as some do not react with excess NH3 at all

37
Q

outline how 2 different transition metal ions can be identified

A

add NH3 or NaOH and the ions will form coloured precipitates

38
Q

why does the precipitate Fe(OH)2 often turn orange-brown on the surface when left standing

A

this is because the Fe2+ gets oxidised to Fe3+ in the air, and Fe(OH)3 is an orange-brown colour

39
Q

give an example of a complex metal ion in the body

A

haemoglobin
- it consists of a central Fe2+ metal ion with a multidentate haem ring containing 4 nitrogens that form 4 dative bonds in a square planar configuration
- the Fe2+ ion forms one other dative bond with the rest of the protein
- this leaves 1 last spot allowing O2 to reversibly bond with the central Fe2+ ion, allowing it to be carried around the body
- this forms oxyhaemoglobin

40
Q

why is CO dangerous in terms of ligand exchange

A

CO has a lone pair of electrons therefore it can act as a ligand, and it forms a much stronger dative bond with Fe2+ than O2
- if CO is present, it can replace via ligand exchange to form carboxyhaemoglobin

41
Q

what occurs in a reaction between Fe2+ and MnO4-

A

Fe2+ is oxidised to Fe3+
MnO4- is reduced to Mn2+
- causes a purple to colourless colour change

42
Q

what occurs in a reaction between Fe3+ and I-

A

Fe3+ is reduced to Fe2+
I- is oxidised to I2
- causes a colourless to brown colour change - overpowers the iron colour change

43
Q

what occurs in a reaction between Cr2O7 2- and Zn

A

Zn is oxidised to Zn2+
Cr2O7 2- is reduced to Cr3+
- this causes an orange to green colour change
in excess of Zn this can be further reduced to Cr2+ which is pale blue

44
Q

what occurs in a reaction between Cr3+ and hot H2O2

A

Cr3+ is oxidised to CrO4 2-
- this causes a green to yellow colour change
O is reduced in H2O2 to CrO4 2-

45
Q

what occurs in a reaction between Cu2+ and I-

A

Cu2+ is reduced to Cu+, which then forms CuI
- this causes a change form a pale blue solution to a white precipitate (CuI)
I- is oxidised to I2
- this causes a colour change from colourless to brown - mostly this is what is observed

46
Q

what occurs in the reaction between hot Cu2O and H2SO4 + what type of reaction is it

A

Cu is reduced from Cu2O to Cu
- this forms a brown solid
Cu is also oxidised from Cu2O to CuSO4
- this forms a blue solution

this is a disproportionation reaction

47
Q

what type of reaction forms a precipitate

A

precipitation reaction

48
Q

what occurs in a reaction between CrO4 2- and acid

A

CrO4 2- will turn into Cr2O7 2- (oxidation state stays the same)

chemistry module 5 (5 decks)

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