✅15 - Transition Metals Flashcards
Where are transition metals found in the periodic table?
D block
What are transition metals?
D block elements that can form one or more stable ions with partially filled d-orbitals
Which d block period 4 elements are not transition metals?
Scandium and Zinc
How many electrons can the d orbital hold?
10
When ions are formed, which electrons are removed first?
The s electrons
Why is Scandium not a transition metal?
It only forms one ion, Sc3+, which has an empty d subshell
Why is zinc not a transition metal?
It only forms one ion, Zn2+, which has a full d subshell
How many stable oxidation states does Vanadium have?
4
What are the stable oxidation states of Vanadium?
II, III, IV, V
What kind of oxidation state do transition metals have?
Variable oxidation states
What requirements are needed to create a compound or complex with an ion in a specific oxidation state?
The energy given out when forming the compound or the complex is greater than ionisation energy.
How do transition metals form ions?
By loosing electrons from their 4s and 3d subshells
When does the energy released in the formation of a complex or compound by an ion become greater?
When the ionic charge increases.
What are complex ions?
Metal ions surrounded by datively covalently bonded ligands
What is a ligand?
An atom, ion or molecule which donates a pair of electrons to a central metal atom or ion.
What are monodentate ligands?
Molecules that donate 1 lone pair of electrons and form 1 coordinate bond to a central metal ion or metal.
What are bidentate ligands?
molecules that donate two pairs of electrons to a central metal atom or ion, forming two coordinate bonds.
What are multidentate ligands?
Multidentate ligands are molecules or ions that donate multiple pairs of electrons to a central metal atom or ion, forming several coordinate bonds.
What are examples of monodentate ligands?
H2O, NH3, Cl-
What is an example of a multidentate ligands?
EDTA 4-, Oxalate ion (C₂O₄²⁻)
What is the name for water in a complex?
Aqua
What is the name for a hydroide group in a complex? Hydroid is when H has 1- oxidation state e.g (NaH)
hydroxo
What is the name for ammonia in a complex?
Ammine
What is the name for chloride in a complex?
Chloro
How many colours traditionally make up white light?
7
Why are transition metal complexes coloured?
Electrons split into two energy levels when ligands attach. If an electron absorbs light, it can move to a higher energy level, and the light reflected is the colour seen
With 6 ligands, what shape is a complex?
Octahedral
With 4 ligands, what shape is a complex?
Tetrahedral or square planar
With 2 ligands, what shape is a complex?
Linear
What is an example of a linear complex?
Tollen’s reagent
What is cis-platin?
An anti-cancer drug which has a square planar shape
What does a cis- prefix indicate?
That the identical ligands are next to each other
What does a trans- prefix indicate?
That the identical ligands are opposite each other
How does cis-platin kill cancer cells?
It forms a bond between the two strands of DNA which prevents them from separating, and therefore prevents replication
How is trans-platin different to cis-platin?
It is toxic and much less effective at targeting cancer
Why does reducing the number of ligands increase stability?
- The system becomes more disordered (increase in ∆S system).
- Fewer, larger ligands release smaller ligands into the solution, increasing entropy (chelate effect).
- Increased entropy makes the complex more thermodynamically stable.
What causes the greatest increase in stability?
Exchanging a monodentate ligand for a multidentate ligand
How is Fe held in haemoglobin?
By forming dative bonds with four nitrogens in the structure, in a square planar
What else is bonded to the Fe in haemoglobin?
Globin (a protein) and Oxygen
Why is carbon monoxide poisonous?
Because the dative bond between carbon monoxide and haemoglobin is stronger than with oxygen, so any CO breathed in will bins with the haemoglobin and not break easily
What is the equation for the reaction between aqueous NaOH and copper(II) sulfate solution?
[Cu(H2O)6]2+ + 2OH- —> [Cu(H2O)4(OH)2] + 2H2O
What colour is [Cu(H2O)4(OH)2]?
Blue precipitate
What is the equation for the reaction between aqueous ammonia and copper (II) sulfate?
[Cu(H2O)6]2+ + 2NH3 —-> [Cu(H2O)4(OH)2] + 2NH4+
What is the equation for the reaction between the blue copper precipitate and aqueous ammonia?
[Cu(H2O)4(OH)2] + 4NH3 —-> [Cu(NH3)4(H2O)2]2+ + 2H2O + 2OH-
What colour is [Cu(NH3)4(H2O)2]2+?
Deep blue solution
What is the equation for the reaction between copper (II) sulfate solution and conc HCl?
{CU(H2O)6]2+ + 4Cl —-> [CuCl4]2- + 6H2O
What is the colour change when hydrochloric acid is added to copper sulfate solution?
- Initial color change: Blue (from ) → Green
- Further change: Green → Yellow
Higher concentration shifts equilibrium, increasing concentration.
What is the equation for the reaction between hexaaquacobalt(II) and aqueous sodium hydroxide?
[Co(H2O)6]2+ + 2OH- —-> [Co(H2O)4(OH)2] + 2H2O
What is the colour change when sodium hydroxide is added to hexaaquacobalt(II)?
Pink solution to blue precipitate
How many reactions occur between hexaaquacobalt(II) and ammonia?
2
What is the acid-base reaction between hexaaquacobalt(II) and NH3?
[Co(H2O)6]2+ + 2NH3 —-> [Co(H2O)4(OH)2] + 2NH4+
What is the equation for the reaction between [Co(H2O)4(OH)2] and NH3?
[Co(H2O)4(OH)2] + 6NH3 —-> [Co(NH3)6]2+ + 4H2O + 2OH-
What is the colour change between hexaaquacobalt(II) and ammonia?
Precipitate dissolves to a yellow solution
What is the colour of the [Co(NH3)6]3+ ion?
Yellow
What is the equation for the reaction between hexaaquacobalt(II) and conc HCl?
[Co(H2O)6]2+ + 4Cl- —-> [CoCl4]2- + 6H2O
What is the colour change when conc HCl is added to the hexaaquacobalt (II) solution?
Pink to blue
What is the equation for the reaction between hexaaquairon(II) and sodium hydroxide?
[Fe(H2O)6]2+ + 2OH- —-> [Fe(H2O)4(OH)2] + 2H2O
What is the colour change in the reaction between hexaaquairon(II) and sodium hydroxide?
Pale green solution forms a green precipitate
What is the equation for the reaction between hexaaquairon(II) and NH3?
[Fe(H2O)6]2+ + 2NH3 —-> [Fe(H2O)4(OH)2] + 2NH4+
What is the equation for the reaction between hexaaquairon(III) and sodium hydroxide?
[Fe(H2O)6]3+ + 3OH- —-> [Fe(H2O)3(OH)3] + 3H2O
What is the colour change for the reaction between hexaaquairon(III) and sodium hydroxide?
Yellow-brown solution forms and brown precipitate
What is the equation for the reaction between hexaaquairon(III) and NH3?
[Fe(H2O)6] + 3NH3 —-> [Fe(H2O)3(OH)3] + 3NH4
What are the colours shown by chromium compounds affected by?
Some compounds have different colours as solids and aqueous solutions
The colour of the solution depends on the concentration
The presence of dissolved oxygen in an aqueous solution can affect the colour seen
What is the equation for the reaction between the hexaaquachromium(III) ion and aqueous sodium hydroxide?
[Cr(H2O)6]3+ + 3OH- —-> [Cr(H2O)3(OH)3] + 3H2O
What is the colour change for the reaction between hexaaquachromium(III) and sodium hydroxide?
Green or violet solutions forms a green precipitate
What is the equation for the reaction between hexaaquachromium(III) and NH3?
[Cr(H2O)6]3+ + 3NH3 —-> [Cr(H2O)3(OH)3] + 3NH4+
What happens to the precipitate [Cr(H2O)3(OH)3] when it is dissolved?
It dissolves to form a green solution of [Cr(H2O)2(OH)4]-
What happens to the precipitate [Cr(H2O)3(OH)3] when excess ammonia is added?
It is slow to dissolve but eventually a violet or purple solution of [Cr(NH3)6]3+ forms
What is the equation for the reaction between [Cr(OH)6]3- and hydrogen peroxide?
2[Cr(OH)6]3- + 3H2O2 —-> 2CrO42- + 2OH- + 8H2O
What is the colour change for the reaction between the chromium complex and hydrogen peroxide?
Green solution to yellow solution
What is hydrogen peroxide?
An oxidising agent
How does the chromate ion change with acidity?
In alkaline solution, the chromate(VI) ions are stable, but in acidic solution the dichromate(VI) are most stable
What colour change is seen if acid is added to chromate ions?
Yellow to orange
What can dichromate(VI) ions be reduced by?
Zinc
What is the equation for the reduction of dichromate ions using zinc?
Cr2O72- + 14H+ +3Zn —-> 2Cr3+ + 7H2O + 3Zn2+
What is the colour change when dichromate ions are reduced?
Orange to green
What is the colour change when Cr3+ is reduced to Cr2+?
Green to blue
What reaction happens when NaOH is added to [Cr(H2O)3(OH)3]?
It forms [Cr(OH)6]3-
What colour are V2+ ions?
Purple
What colour are V3+ ions?
Green
What colour are (VO)2+ ions?
Blue
What colour are (VO2)+ ions?
Yellow
In what compound does vanadium have a +4 oxidation number?
(VO)2+
In what compound does vanadium have a +5 oxidation number?
(VO2)+
Why is it easy to demonstrate a change in oxidation number with vanadium?
Because its colour changes are so distinctive
What can be used to reduce vanadium from +5 to +2?
Zinc
What is the equation for the reduction of vanadium from +5 to +4?
2(VO2)+ + 4H+ + Zn —-> 2(VO)2+ + Zn2+ + 2H2O
What is the equation for the reduction of vanadium from +4 to +3?
2(VO)2+ + 4H+ + Zn —-> 2V3+ + Zn2+ + 2H2O
What is the equation for the reduction of vanadium from +3 to +2?
2V3+ + Zn —-> 2V2+ + Zn2+
What is the equation for the reduction of vanadium from +2 to 0?
2V2+ + Zn —-> 2V + Zn2+
Which of the vanadium reductions is not thermodynamically feasible?
+2 to 0
In what state are transition metals usually used as catalysts?
Solid, as a powder
What is the catalyst in the contact process?
V2O5 - Vanadium Pentoxide
What are the steps of surface adsorption theory?
Adsorption
Reaction
Desorption
What is adsorption?
One or more reactants become attached to the catalyst
What is the reaction step in surface adsorption theory?
Following the weakening of the bonds in the adsorbed reactants
What is desorption?
The reaction product becomes detached from the surface of the catalyst
What are the reactions that occur on the surface of vanadium in the contact process?
V2O5 + SO2 —-> V2O4 + SO3
V2O4 + 0.5O2 —-> V2O5
What are the problems tackled by catalytic converters?
Increased pollution levels
Carbon monoxide emissions
Nitrogen monoxide emissions
What are the transition metals used in catalytic converters?
Platinum and rhodium, sometimes palladium
What is the equation for the reaction between Carbon monoxide and nitrogen monoxide?
2CO + 2NO —-> 2CO2 + N2
Why does the reaction between CO and NO occur on catalytic converters?
Because the molecules of CO and NO are adsorbed and then, because their bonds are weakened, they react together to form CO2 and N2, which are then desorbed
What is a key feature of homogeneous catalysts?
The formation of an intermediate species for which a specific formula can be written
What is the equation for the reaction between persulfate ions and iodide ions?
S2O82- + 2I- —-> 2SO42- + I2
What is the catalyst in the reaction between iodide and persulfate ions?
Fe2+
What are the steps in the reaction between I- and S2O82-?
S2O82- and 2Fe2+ react together to form 2SO42- and 2Fe3+
2Fe3+ react with 2I- to form 2Fe2+ and I2
Why do the Fe2+ and S2O82- react together?
Because they do not repel each other, as they have the opposite charge
What is the alternative mechanism for the reaction between I- and S2O82-?
2Fe3+ + 2I- —-> 2Fe2+ + I2
S2O82- + 2Fe2+ —-> 2SO42- + 2Fe3+
Why do transition metals show variable oxidation states?
✅ Close Energy Levels – 3d and 4s orbitals have similar energy, allowing multiple electron losses.
✅ Partial Filling of d-Orbitals – Incomplete d-subshell enables different oxidation states.
✅ Stable Configurations – Half-filled (d⁵) or fully filled (d¹⁰) d-orbitals enhance stability.
Why do transition metals show variable oxidation states?
- Close Energy Levels – 3d and 4s orbitals have similar energy, allowing multiple electron losses.
- Partial Filling of d-Orbitals – Incomplete d-subshell enables different oxidation states.
- Stable Configurations – Half-filled (d⁵) or fully filled (d¹⁰) d-orbitals enhance stability.
Why do transition metals show variable oxidation states?
- Close Energy Levels – 3d and 4s orbitals have similar energy, allowing multiple electron losses.
- Partial Filling of d-Orbitals – Incomplete d-subshell enables different oxidation states.
- Stable Configurations – Half-filled (d⁵) or fully filled (d¹⁰) d-orbitals enhance stability.
what is Autocatalysis?
Process whereby one of the products in one reaction catalyses the further reaction of the catalysts.
what is the chelating effect?
special stability that comes with the formation of a metal complex containing a polydentate ligand when compared to a monodentate ligand.
