inorganic - transition metals 2

Question 1

ligand

Answer 1

a ligand is a molecule or ion that forms a co-ordinate bond with a transition metal ion by donating a pair of electrons

Question 2

co-ordination number

Answer 2

co-ordination number is number of co-ordinate bonds to the central metal atom or ion

Question 3

complex

Answer 3

a complex is a central transition metal atom or ion surrounded by ligands that are bonded to it by co-ordinate bonds

Question 4

co-ordinate bonds

Answer 4

a covalent chemical bond that is produced when one atom shares a pair of electrons (ligand) with another atom lacking such a pair (transition element)

Question 5

mono/unidentate ligand

Answer 5

a ligand that forms ONE co-ordinate bond to the central transition metal ion/atom (donates one pair of electrons)

Question 6

examples of monodentate ligands

Answer 6

Cl- chloride ion
H2O water
NH3 ammonia
CN- cynide

Question 7

bidentate ligand

Answer 7

a ligand that forms TWO co-ordinate bonds to the central transition metal ion/atom (donates two pairs of electrons)

Question 8

examples of bidentate ligands

Answer 8

C2O4 2- ethanedioate ion (oxalate)
NH2CH2CH2NH2:
- ethylene diamine-1,2-diaminoethane
- ethane-1,2-diamine

Question 9

multidentate ligand

Answer 9

a ligand that forms THREE or MORE co-ordinate bonds to the central transition metal ion/atom (donates more than two pairs of electrons)

Question 10

give examples of multi dentate ligands

Answer 10

EDTA4– ethylenediaminetetraacetate

- it forms 6 coordinate bonds

Question 11

aqua ions

Answer 11

• the salt of a transition metal is dissolved in water
• the positively charged metal ion becomes surrounded by water molecules that act as ligands - because water molecules are attracted to it
• normally there are six water molecules acting as ligands in an octahedral arrangement

Question 12

shape of ions with co-ordination number of 6

Answer 12

octahedral
e.g. [Co(NH3)6]3+
[Cu(H2O)6]2+

Question 13

shape of ions with co-ordination number of 4

Answer 13

tetrahedral
e.g. [CoCl4]2-
[FeCl4]-

Question 14

SOME ions with a co-ordination number of 4 have a shape of

Answer 14

square planar
e.g. [NiCN4]2-
[Pt(NH3)2Cl2]

Question 15

ligands of NH3 and H2O

Answer 15

• they are similar of size
• uncharged
• if any exchange occurs between both ligands, there is no change in co-ordination number
• smaller than Cl-

Question 16

chelate

Answer 16

• complex ions with polydentate ligands

- chelates are much more stable than complex ions formed with monodentate ligands

Question 17

chloride ion complex ions

Answer 17

• chloride ions are large so only 4 can fit around the transition metal ion
• co-ordination number = -4 as they form 4 co-ordinate bonds
• chloride ions are charged so have an impact on the overall charge
• the complex has a tetrahedral shape with bond angles of 109.5°

Question 18

ammonia/water complex ions

Answer 18

• both molecules are small so 6 can fit around the transition metal ion
• co-ordination number = +6 as they form 6 co-ordinate bonds
• both molecules are uncharged so have no impact on the overall charge
• the complex has an octahedral shape with bond angles of 90°

Question 19

ethanedioate (oxalate) ion and ethane-1,2-diamine complex ions

Answer 19

• 3 ligands fit around the transition metal ion, each forming 2 co-ordinate bonds
• co-ordination number = -6
• the complex has an octahedral shape with bonds angles of 90°

Question 20

the chelate effect

Answer 20

• if a bidentate/multidentate ligand is added to a transition metal ion complex containing only monodentate ligands
• the multidentate ligands will exchange with the monodentate ligands
  e.g.
  [Cu(H2O)6]2+(aq) + EDTA-4(aq)  [CuEDTA]2-(aq)+ 6H2O(l)
  there are 2 species on the left, 7 species on the right
• the result of an increase in the number of particles will cause an increase in entropy which drives the reaction to the right
• but there is little enthalpy change

Question 21

why are chelate complexes with polydentate ligands favoured over complexes with monodentate ligands

Answer 21

• reversing the reaction will be difficult in terms of entropy
• if we use our Gibbs free-energy equation:
  ΔG = ΔH – TΔS
  we can see that a small positive or negative ΔH value and a large ΔS value is likely to give us a large negative ΔG – so the substitution will occur

Question 22

haemoglobin

Answer 22

• contains 4 haem groups
• each haem group contains an Fe(ii) 2+ ion
• Fe2+ ions have a co-ordination number of 6

Question 23

why is carbon monoxide toxic

Answer 23

it replaces oxygen co-ordinately bonded to Fe(II) in haemoglobin

Question 24

Tollen’s reagent

Answer 24

• Ag+ silver ions form a linear complex with NH3

[Ag(NH3)2]+

Question 25

what type of isomerism do octahedral and square planar complexes display

Answer 25

• cis-trans isomerism (E–Z isomerism) with monodentate ligands

Question 26

cis-trans isomerism (E–Z isomerism) arises when

Answer 26

• when they ligands are either close to each other or on opposite sides of the central metal ion
• cis (Z) implies that ligands are close to each other
• trans (E) implies that ligands are on opposite sides

Question 27

Platin

Answer 27

• square planar complex ion
  [CrCl2(H2O)4]+
• displays cis-trans isomerism

Question 28

cis-Platin

Answer 28

• one of the most successful anti-cancer drugs

- however its opposite isomer, trans-Platin shows no therapeutical effect

Question 29

why are the effects of cis-Platin and trans-Platin different

Answer 29

cis-trans isomers have different chemical properties

Question 30

what type of complexes display optical isomerism

Answer 30

• octahedral complex ions with two or more bidentate ligands

Question 31

optical isomerism arises when

Answer 31

• when there are two isomers whose mirror image is nonsuperimposable

Question 32

examples of complexes that will show optical isomerism

Answer 32

[Ni(NH2CH2CH2NH2)3]2+

[Cr(C2O4)3]3-