TM - Pack 1

• What is transition metal ?

  > metal that can form one or more stable ions with an incomplete d- sub shell
• Which elements are not transition metals and why ?

  > Sc + Zn don't form stable ions with an incomplete d sub-shell
• What are the 4 characteristic properties of transition metals

  > complex formation

  
  

  > formation of coloured ions

  
  

  > Catalytic activity

  
  

  > variable oxidation state

  
  

  (arise due to incomplete d-subshell)
• What is a complex

  > a central metal ion surrounded by ligands
• What is a ligand?

  > molecule or ion that forms a co-ordinate bond with a transition metal by donating a pair of e-
• What are monodentate ligands

  > molecules or ions that donate 1 electron pair to central metal ion to form 1 CO-ORDINATE BOND

  
  

  
  

  e.g H2O, NH3, Cl- and CN-
• What are bidentate ligands?

  > molecules or ions that have two atoms that EACH donate an electron pair to central metal ion

  
  

  > to form 2 co-ordiante bonds

  
  

  (H2NCH2CH2NH2)

  (C2O42-)
• What are multidentate ligands

  - molecules or ions that have more than 2 atoms that each donate an electron pair to central metal ion

  
  

  
  

  > to form more than 2 co-ordinate bonds

  
  

  (EDTA4-) has 6 atoms + forms 6 co-ordiante bonds
• What is a co-ordiantion number ?

  > number of co-ordinate bonds to central metal atom or ion
• Bond angle + co-ordiantion number of octahedral

  > 90

  
  

  > 6
• Bond angle + co-ord number of tetrahedral

  > 109.5

  
  

  > 4
• Bond angle + co-ord number of square planar

  > 90

  
  

  > 4

  
  

  (Pt, Pd, Ni)
• bond angle + co-ord number of linear

  > 180

  
  

  > 2
• Complexes containing Cl- ligands usually have a co-ordination of 4 and are tetrahedral shape . WHY

  > Cl- ligand bigger than H2O + NH3
• Substitution of ligands of a similar size

  > ligands NH3+ H2O similar In size

  
  

  > so when ligand substitution occurs co-ordination number+ shape don't change
• Colour change when aqueous cobalt salts are reacted with excess NH3 (all six water ligands replaced)

  From pink to pale brown
• Colour change when aqueous copper salts reacted with excess NH3 (four water ligands replaced)

  Blue---> Deep blue
• Colour change when aqueous cobalt salts reacted with conc HCl (all six water ligands replaced)

  Pink ----> Blue

  
  

  Co-ord number from 6 to 4

  
  

  > octahedral to tetrahedral
• Colour change when aqueous copper salts reacted with conc HCl

  Blue----> yellow (green)
• Structure of Haem


  > iron(II) complex with multi dentate ligand

  
  

  > co-ordiantion number of 4

  
  

  > shape around iron (II) in haem unit = square planar
• Describe CO poisoning


  > when CO inhaled haemoglobin can substitute water ligands for CO ligands

  
  

  > bond between CO + Fe(II) is very strong + not readily reversed

  
  

  > prevents O2 being bonded to Hb

  
  

  > CO considered toxic
• What is the chelate effect

  >When multidentate + bidentate ligands replace mono dentate ligands

  
  

  > to form stable complexes
• Why are transition metals coloured?

  > incomplete d-subshell
• Why do the colour of TM arise ?

  > TM can absorb certain frequencies of visible light

  
  

  > causes d-electrons to be promoted

  
  

  > remaining colours of light TRANSMITTED
• Why are aqueous copper (II) ions blue in colour?

  > Cu2+ absorb a certain frequency of visible light

  
  

  > d electrons promoted

  
  

  > blue light transmitted
• △E (J) equation with h and v


  △E = hv

  
  

  h --> Plank's constant (6.63 x 10-34) Jd

  
  

  v---> frequency of visible light absorbed Hz/s-1
• v equation with c and λ

  v = c / λ

  
  

  c --> speed of light

  3 x 10 ^8

  
  

  λ --> wavelength of light (in m )
• energy gap equation :

  ∆E = h x c/λ

  
  

  h = plank's constant

  
  

  c = speed of light

  
  

  λ = wavelength of light
• How to convert nm into m

  x 10^ -9

  
  

  1nm = 1 x 10 ^-9m
• Which factors (if changed) affect the colour of TM complexes

  > change in ligand

  
  

  > change in co-ordination number

  
  

  > change in oxidation state
• Change in Ligand

  [Ni(H2O)6]2+ + 6NH3 --> [Ni (NH3)6]2+ + 6H2O

  
  

  colour change: Green to Blue
• Change in oxidation state

  [ Fe(H2O)6] 2+ ---> [ Fe(H2O)6]3+

  
  

  colour change from green to yellow- brown
• what is spectroscopy?

  > study of how electromagnetic radiation interacts with matter

  
  

  > colorimetery is a type of spectroscopy

  
  

  > colorimeter measures amount of light absorbed by as sol - conc
• how to find conc of unknown - calibration curve

  > create 4 or 5 standard solutions of known conc

  
  

  > select filter of complementary colour + measure absorbance of known solutions

  
  

  > unknowns absorbance can be measured + found from cali curve
• what are stereoisomers


  > Compounds with the same structural formula but a different arrangement of atoms in space
• which shapes of complexes can exhibit stereoisomers?

  > square planar + octahedral

  
  

  when square planar has 2 dif ligands cis-trans isomers can form

  
  

  cis = 90 apart

  
  

  Trans = 180 apart
• octahedral cis trans


  > two dif ligands four of one and 2 of another

  
• What other isomers can octahedral complexes form ?

  > Optical (non-superimposable mirror images)

  
  

  >occurs when bidentate ligands present