Complexes

Question 1

How do transition metal ions form co-ordinate bonds?

Answer 1

by accepting electron pairs from ions or molecules

Question 2

What is a complex ion>

Answer 2

• when two, four, or six ligands bond to a single transition metal ion

Question 3

What is the co-ordination number

Answer 3

no. of co-ordinate bonds with ligands that surround the TM

Question 4

What is a ligand?>

Answer 4

• ion or mlecule w lone pair of electrons that forms a co-ordnate bond with a transition metal
• acts as as lewis base

Question 5

What are aqua ions?

Answer 5

• dissolve salt of a transition metal in water
• water acts as ligand
• usually in an octahedral arrangement
• such species are called aqua ions

Question 6

What are the different shapes of complex ions?

Answer 6

• octahedral
  
  • co-ordination number of six
• most tetrahedral
  
  • co-ordination number of four
  • some square plane
    
    • co-ordination number of four

Question 7

What are multidentate ligands?

Answer 7

• have more than one atom with a lone pair of electrons which can bind to a transition metal ion

Question 8

What are chelates?

Answer 8

• complex ions with polydenate ligands are called chelates

Question 9

What are chelates used for?

Answer 9

remove d-block metal ions from solutions

Question 10

What is EDTA?

Answer 10

• a hexadentate ligand
• iff added to a soln of a transition metal salt, the EDTA will replace all six water ligands

Question 11

What is the chelate effect?

Answer 11

• in reaction w a hexdentate ligand, e.g. EDTA, two species are replaced by 7
  
  • 6 water molc released
• causes increase in entropy
  
  • drives reaction to right
• chelate complexes w polydenate ligands are favoured over complexes w mondentate ligands
• this is the chelate effect

Question 12

What reasons are there for changes in shape?

Answer 12

• size of ligand forming bond
  
  • e.g Cl > N, forms fewer ligands fit round central metal ions

Question 13

What cis and trans complexes

Answer 13

• no way for rotation to occur
• cis means the 2 of the same molc are next to eachother rather than opposite

Question 14

How does optical isomerism occur?

Answer 14

• two isomers than are non-superimposible mirror images
• occur when there are two or more bidentate ligands in a complex
• chiral
• idnetical properties
  
  • different effect on polarised light

Question 15

Why does ammonia replace water?

Answer 15

• similar in size
  
  • no change in co-ordination number
• reacts with hexaaqua ions in distinct ways because it acts as a base and a ligand
• metal hydoxide forms when lil bit of NH3 added
  
  • when more added the ppt redissolves and ligan exchange reaction has occured

Question 16

What is haem? How does it transport oxygen>

Answer 16

• an iron(II) complex w a muldebtate ligand and a globin
• oxygen forms a co-ordinate bond bond to Fe(II) in haemoglobin, enabling oxygen to transport in the blood
• CO is toxic because it replaces oxygen co-ordinately bonded to Fe(II) in haemoglobin

Question 17

Why does the ppt dissolve when ammonia added?

Answer 17

Question 18

What is an example of a linear and square planar complex?

Answer 18

• linear
  
  • [Ag(NH₃)₂]⁺
• square planar
  
  • [PtCl₂(NH₃)₂]
  • (cisplatin)