5.3.1 Transition elements Flashcards
Definition of a transition element?
A d-block element that forms at least one ion with a partially filled d-subshell.
Properties of a transition element. (7)
Contains metallic bonding: high melting and boiling points.
Hard
Shiny
High density
Forms coloured compounds
Has different oxidation stages when in a compound.
Their elements and compounds can act as catalysts.
Why is scandium not a transition element?
Sc only forms one ion: Sc3+
This ion has no electrons in the d- subshell.
Why is Zinc not a transition element?
Only forms one ion: Zn2+
Since the 4S sub-shell empties before the 3d sub-shell, the 3d sub-shell is filled.
Fully filled d-sub shell, therefore cannot be a transition element.
What is the electronic configuration of Chromium and why is it like this?
[Ar] 4s^1 3d^5
The 3d sub-shell prefers having a half occupied/ fully occupied sub- shell due to spin pair repulsion/ stability.
What is the electronic configuration of Copper and why is it like this?
[Ar] 4s^1 3d^10
The 3d sub-shell prefers having a fully occupied sub- shell due to stability so an electron is removed from the 4s sub-shell.
What is a complex ion?
Central metal ion surrounded by ligands.
What is a ligand?
Molecule/ ion that donates a pair of electrons to metal ion to form a dative covalent bond/ co-ordinate bond.
What are the coloured compounds of Fe2+ and Fe3+
Fe2+: pale green
Fe3+: yellow
What are the coloured compounds of Cr3+ and Cr6+
Cr3+: green
Cr6+: yellow/ orange
Give four examples of how transition metals act as heterogeneous catalysts.
Haber process: Solid iron catalyst used
Contact process, SO2 + O2: Solid V2O2 used
Hydrogenation: solid Nickel catalyst used.
Decomposition of hydrogen peroxide: Manganese (IV) oxide solid is used (MnO2)
Give an example of how a transition metal acts as a homogeneous catalyst.
Reaction between iodide ions and peroxodisulfate ions:
Fe3+ (aq) catalyst used.
What is a monodentate ligand?
A ligand that donates ONE pair of electrons to a central metal ion.
What is the shape of a complex ion with a co-ordinate number of six?
Octahedral: 90 degree bond angle.
Shape of a complex ion with co-ordinate number:
2
4
5
2: linear- 180 degrees
4: tetrahedral (109.5 degree)/ square-planar- 90 degrees
5: trigonal bipyramidal- 90 and 120 degrees
What type of isomerism can occur in complex ions?
Stereoisomerism:
Optical
Cis-Trans
Cis-Trans isomerism in complex ions.
Can occur in complex ions with:
4/6 co-ordinate bonds that are monodentate, with 2 different monodentate
6 co-ordinate bonds with monodentate and/or bidentate ligands
Cis- Same ligands are adjacent (90 degrees)
Trans- Same ligands are opposite (180 degree)
Optical isomerism in complex ions.
Occurs in complex ions with:
6 co-ordinate bonds that contains two or more bidentate ligands.
Trans isomers are not optical isomers as they form symmetrical molecules.
How can you differentiate between two complex ion, optical isomers?
Pass the molecules through plane polarised light.
Each isomer will rotate the light in a different direction.
Describe Platin and how it is used in medicine.
Platin: Pt(NH3)Cl2
Cis-Platin is used in chemotherapy to shrink and stop cancerous growth.
Cis-Platin attaches to DNA and prevents DNA replication which prevents cell division.
This leads to cell mechanism uniting apoptosis.
However: negative side effects include kidney damage
Describe how haemoglobin uses a complex ion?
Contains haem group:
Fe2+ and porphyrin ring with 4 nitrogens
This forms an octahedral structure with two bonds free.
One bond can attach to a polypeptide in a protein.
Another bond can attach to a molecule of oxygen.
Carbon monoxide can displace oxygen as it form a strong bond with Fe2+
Describe the reaction between Copper (II) and OH-
Precipitation reaction:
Copper solution is original light blue
A light blue Copper Hydroxide precipitate forms. This is not soluble in excess OH-
This ppt is soluble in excess ammonia to form a deep blue solution: Cu(NH3)4 (H2O)2
Colour of Cu2+ solution
Light blue
Colour of Cu(OH)2 precipitate
Light blue
Colour of Cu(NH3)4(H2O)2
Deep blue
Describe the reaction of Mn2+ with hydroxide ions
Mn2+ is originally a pale pink solution
It forms a light brown precipitate: Mn(OH)2
Pale pink—> light brown
Precipitate is not soluble in excess OH-
Describe the reaction between Fe2+ and hydroxide ions
Fe2+ is originally a green solution
It forms a green precipitate: Fe(OH)2
Green —-> green ppt
Precipitate is not soluble in excess OH-
Precipitate can be oxidised to an orange brown ppt—> Fe(OH)3
Reaction between Fe3+ and hydroxide ions
Fe3+ is originally a yellow solution
An orange/ brown precipitate forms
Yellow —> orange/brown
The precipitate is not soluble in excess OH-
Reaction between Cr3+ and hydroxide ions
Cr3+ is originally a violet solution
It forms a grey-green ppt: Cr(OH)3
It is soluble in excess NH3: forms purple solution
Also soluble in excess OH-: forms dark green solution
Describe the qualitative analysis when oxidising Fe2+
Fe2+ is reacted with MnO4-, an oxidising agent.
MnO4- is added in a burette and is initially purple.
A colour change from colourless to light pink the the conical flask confirms the end point.
Describe the qualitative analysis when reducing Fe3+
Iodide ions are used as a reducing agent.
Fe3+ is originally orange/brown.
The solution turns brown as Iodide ions are oxidised to Iodine.
Fe3+ is reduced to Fe2+ (which is pale green).
Describe the qualitative analysis when reducing Cr2O7 2-
Zinc is used as a reducing agent, with HCl or H2SO4.
Dichromate is originally orange but then is reduced to a green colour- Cr3+
This is further reduced to Cr2+ which forms a pale blue solution. This only occurs when there is an excess of zinc.
Describe the qualitative analysis when oxidising Cr3+
Cr3+ is reacted with hot, alkaline Hydrogen peroxide.
Cr3+ is oxidised with hydroxide ions and H2O2.
This shows a colour change from green to orange (CrO4 2-).
Describe the qualitative analysis when reducing Cu2+.
Cu2+ reacts with excess iodide ions.
Iodide ions are oxidised to iodine, which forms a brown solution.
Cu2+ is originally pale blue but a white precipitate forms when CuI(s) is formed.
