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 acid-base reaction of [Cu(H2O)6]2+ (from copper sulfate solution) with aqueous sodium hydroxide
State observations
[Cu(H2O)6]2+ + 2OH- ——-> [Cu(H2O)4(OH)2] + 2H2O
Pale blue solution forms a pale blue precipitate
Give the equation for the acid-base reaction of [Cu(H2O)6]2+ (from copper sulfate solution) with aqueous ammonia
State observations
[Cu(H2O)6]2+ + 2NH3 ——> [Cu(H2O)4(OH)2] + 2NH4+
Pale blue solution forms blue precipitate
Give the equation for when aqueous ammonia is added to the blue ppt caused by formation of [Cu(H2O)4(OH)2]
State observations
[Cu(H2O)4(OH)2] + 4NH3 ——> [Cu(NH3)4(H2O)2]2+ + 2H2O. +. 2OH-
Blue precipitate dissolves go for a deep blue solution
Give the equation for the change in coordination number reaction of [Cu(H2O)6]2+ (from copper(II) sulfate solution) 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 equation for the reaction of a hexaaquacobalt(II) ion with aqueous sodium hydroxide
State the colour change seen
[Co(H2O)6]2+. +. 2OH-. ——>. [Co(H2O)4(OH)2]. + 2H2O
Pink solution forms blue precipitate
Give the equation for the reaction of a hexaaquacobalt(II) ion with aqueous ammonia
State the colour change seen
[Co(H2O)6]2+. +. 2NH3. ——>. [Co(H2O)4(OH)2]. + 2NH4+
Pink solution forms blue precipitate
Give the equation for the reaction of a hexaaquacobalt(II) ion with aqueous ammonia is added in excess
State the colour change seen
What happens upon standing
[Co(H2O)4(OH)2]2+. +. 6NH3. ——>. [Co(NH3)6]2+. + 4H2O. + 2OH-
Blue ppt dissolves to form a brown solution
Upon standing the brown solution changes colour because of oxidation) by o2 in atmosphere ( oxidation number of cobalt increases from +2 to +3 and yellow [Co(NH3)6]3+ ion forms )
Give the equation for the reaction of a hexaaquacobalt(II) ion with concentrated HCl
State the colour change seen
[Co(H2O)6]2+. +. 4Cl- ——->. [CoCl4]2- +. 6H2O
Pink solution turns blue
Give the equation for the reaction of a hexaaquairon(II) ion with aqueous sodium hydroxide
State the colour change seen
[Fe(H2O)6]2+. +. 2OH- ——->. [Fe(H2O)4(OH)2]. +. 2H2O
Pale green solution forms green precipitate
Give the equation for the reaction of a hexaaquairon(II) ion with aqueous ammonia
State the colour change seen
What happens upon standing ?
[Fe(H2O)6]2+. +. 2NH3. ——->. [Fe(H2O)4(OH)2]. +. 2NH4+
pale green solution forms green precipitate
Upon standing the colour of the green ppt gradually changes to brown as o2 in atmosphere causes oxidation forming [Fe(H2O)3(OH)3]
Give the equation for the reaction of a hexaaquairon(III) ion with aqueous sodium hydroxide
State the colour change seen
[Fe(H2O)6]3+ +. 3OH- ——> [Fe(H2O)3(OH)3]. +. 3H2O
Yellow brown solution forms a brown precipitate
Give the equation for the reaction of a hexaaquairon(III) ion with aqueous ammonia
State the colour change seen
[Fe(H2O)6]3+ +. 3NH3. ——> [Fe(H2O)3(OH)3]. +. 3NH4+
Yellow-brown solution forms brown precipitate
