Topic 15: Transition Metals Flashcards
Define transition metals
D-block elements that form one or more stable ions with incompletely filled d-orbitals
Give the characteristics of transition metals
- hard solids
- high melting and boiling temperatures
- can act as catalysts
- form coloured ions and compounds
- form ions with different oxidation numbers
- form ions with incompletely filled d-orbitals
The relatively small size of a transition metals enables them to…
Attract electron-rich species more strongly including water molecules present in aq solutions
Describe how the structure of a ligand is drawn
- bonds are shown with arrow heads indicating dative bonds
- whole structure drawn inside square brackets and the original charge of the ion is shown outside the brackets
What is the coordination number
The total number of dative bonds around the metal ion
Define ligand
A species that uses a lone pair of electrons to form a dative bind with a metal ion
Define complex
A species containing a metal ion joined to ligands
Define complex ion
A complex with an overall positive or negative charge
Explain how complexes are named
In order:
- number of ligands eg. hexa
- name of ligand eg. aqua
- name of metal ion eg. iron
- oxidation number of the metal ion eg. (II)
Give the stock answer for the following question:
Explain why the solution is coloured
Water ligand causes 3d orbital to split into 2 energy levels
Electrons in the lower energy level absorb energy from the visible spectrum and are executed to a higher energy level
(**) light is transmitted as its complementary colour is absorbed
Give 2 examples of a square planar complex
xenon tetrafluoride XeF4
cis-platin
Describe the cis and trans isomers of cis-platin
Cis = identical ligands are next to eachother, Trans = opposite
Cis-platin consists of a platinum (II) ion, two ammonia ligands and two chloride ion ligands
Explain briefly the anti-cancer action of cis-platin
- all cells including cancer cells contain DNA
- during cell division the 2 strands of DNA must separate from eachother to form more DNA
- the structure of cis-platin enables it to form a bond between the 2 strands of DNA, preventing them from separating & so prevents the cancer cells from dividing
Define monodentate, bidentate and multidentate ligands
Monodentate ligands are ones that form one dative bond with a metal ion
Bidentate ligands form 2 dative binds with a metal ion
Multidentate ligands form several dative bonds with a metal ion
What is the most common bidentate ligand
NH2CH2CH2NH2 (1,2 diaminoethane) sometimes abbreviated to en
What is the most common multidentate ligand
EDTA (6 dative bonds)
What is the effect on the stability of a complex when a ligand exchange reaction takes place ?
If the total number of species (ligands) increases, the system becomes more disordered
As a result there is an increase in △S(system)
Formation of products is favoured due to their increased stability compared to reactants
How does the oxygen molecule act as a ligand in haemoglobin
When haemoglobin collects oxygen, oxygen uses one of its lone pairs of electrons to form a dative bond with one of the Fe2+ ions
Explain the effect of carbon monoxide on haemoglobin
- Carbon monoxide has a lone pair of electrons on its carbon atom that enables it to act as a ligand
- The strength of the dative bond between oxygen and haemoglobin < strength of dative bond between carbon monoxide and haemoglobin
- Therefore any carbon monoxide breathed in is likely to replace the oxygen in a ligand substitution reaction
- The oxygen carrying capacity of the blood is reduced as the dative bond is so strong that it does not break easily
What are the 4 main types of reaction that can occur with transition metal ions causing a change in colour
- redox : change in oxidation number of metal cation
- acid-base reaction : one or more of the ligands loses/gains hydrogen
- ligand exchange : substitution of one or more of the ligands around the transition metal ion
- coordination number change : number of ligands changes
Give the equation for the change in coordination number reaction Cu2+ ion with concentrated HCl
State observations
[Cu(H2O)6]2+. +. 4Cl- ——> [Cu(Cl)4]2- +. 6H2O
Acid is added slowly and continuously - colour gradually changes from blue to green to yellow
Give the equations and colour changes for reaction of Cr3+ ion with OH- and excess OH-
With OH- : [Cr(H2O)6]3+. +. 3OH- ——>. [Cr(H2O)3(OH)3]. +. 3H2O
violet solution - green ppt
With excess OH- : [Cr(H2O)3(OH)3]. + OH- ——>. [Cr(H2O)2(OH)4]- +. H2O
green ppt - green solution
Give the equations and colour changes for reaction of Fe2+ ion with OH- and excess OH-
With OH- : [Fe(H2O)6]2+. +. 2OH- ——> [Fe(H2O)4(OH)2] +. 2H2O
pale green solution - green ppt
With excess OH- : no further change
Give the equations and colour changes for reaction of Fe3+ ion with OH- and excess OH-
With OH- : [Fe(H2O)6]3+. +. 3OH- ——> [Fe(H2O)3(OH)3] +. 3H2O
yellow-brown solution - brown ppt
With excess OH- : no further change
Give the equations and colour changes for reaction of Co2+ ion with OH- and excess OH-
What happens upon standing ?
With OH- : [Co(H2O)6]2+. +. 2OH- ——> [Co(H2O)4(OH)2] +. 2H2O
pink solution - blue ppt
Upon standing : colour of ppt gradually changes pink
With excess OH- : no further change
Give the equations and colour changes for reaction of Cu2+ ion with OH- and excess OH-
With OH- : [Cu(H2O)6]2+. +. 2OH- ——> [Cu(H2O)4(OH)2] +. 2H2O
pale blue solution - blue ppt
With excess OH- : no further change
Give the equations and colour changes for reaction of Cr3+ ion with NH3 and excess NH3
With NH3 : [Cr(H2O)6]3+. +. 3NH3 ——> [Cr(H2O)3(OH)3] +. 3NH4+
violet solution - green ppt
With excess NH3 : [Cr(H2O)3(OH)3] +. 6NH3. —-> [Cr(NH3)6]3+ +. 3H2O. +. 3OH-
green ppt - purple solution
Give the equations and colour changes for reaction of Fe2+ ion with NH3 and excess NH3
what happens upon standing ?
With NH3 : [Fe(H2O)6]2+. +. 2NH3 ——> [Fe(H2O)4(OH)2] +. 2NH4+
pale green solution - green ppt
Upon standing : colour of green ppt gradually changes to brown as o2 from atmosphere causes oxidation, forming [Fe(H2O)3(OH3)]
With excess NH3 : No further change
Give the equations and colour changes for reaction of Fe3+ ion with NH3 and excess NH3
With NH3 : [Fe(H2O)6]3+. +. 3NH3 ——> [Fe(H2O)3(OH)3] +. 3NH4+
yellow-brown solution - brown ppt
With excess NH3 : No further change
Give the equations and colour changes for reaction of Co2+ ion with NH3 and excess NH3
What happens upon standing
With NH3 : [Co(H2O)6]2+. +. 2NH3 ——> [Co(H2O)4(OH)2] +. 2NH4+
pink solution - blue ppt
With excess NH3 : [Co(H2O)4(OH)2]. +. 6NH3 ——> [Co(NH3)6]2+. +. 4H2O. +. 2OH-
blue ppt - brown solution
Upon standing the brown solution changes colour to yellow because of the oxidation by o2 in the atmosphere. [Co(NH3)6]3+ is formed (ie. oxidation number changes from +2 to +3)
Give the equations and colour changes for reaction of Cu2+ ion with NH3 and excess NH3
With NH3 : [Cu(H2O)6]2+. +. 2NH3 ——> [Cu(H2O)4(OH)2] +. 2NH4+
pale blue solution - blue ppt
With excess NH3 : [Cu(H2O)4(OH)2]. +. 4NH3 ——> [Cu(NH3)4(H2O)2]2+. +. 2H2O. +. 2OH-
blue ppt - dark blue solution
Give the equation for the change in coordination number reaction Co2+ ion with concentrated HCl
State observations
[Co(H2O)6]2+. +. 4Cl- ——> [Co(Cl)4]2- +. 6H2O
Pink solution gradually changes to blue
Give the equation for the oxidation of a Cr3+ ion
State conditions and observations
Providing solutions are alkaline, oxidation is achieved by the addition of hydrogen peroxide (H2O2)
2[Cr(OH)6]3- + 3H2O2. ——>. 2CrO4 2- +. 2OH- +. 8H2O
Solution changes from green to yellow
