Chapter 24 Transition Elements Flashcards by Vinay Ladwa

What are the D block elements?

Elements found between group 2 and group (1)3
Highest energy electron found in a d orbital

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What are the electron configurations of chromium and copper?

Cr= …3d5 4s1
Cu= 3d10 4s1

Half or full d sub shell more stable than not, and so electron excites from the 4s orbtial

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Which orbital for d block elements is removed first?

4s
It’s why a lot of d block elements have 2+ ions
Filling 4s first, also empties first as the energy of the 3d falls below that of the 4s when both are filled

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What is the definition for transition metals? What D block elements do not count as transition metals?

D block elements that form at least 1 ion with a partially full d-orbital

Zinc - only Zn2+ so a full d sub shell
Sc- not Sc3+, so an empty d sub shell

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What are the colours of chromium in various oxidation states?

Cr2+ = light blue
Cr3+ = dark Green
Cr4+ and Cr5+ = colourless
Cr6+ = orange or yellow

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What is the link between oxidation state and oxidising potential?

Transition metals in high oxidation states are good oxidising agents as the metal complex wants to be reduced
E.g MnO4- +7 wants to be Mn2+

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What are some examples of transition metals as catalysts?

Haber Process- N2 + 3H2 —/2NH3. Catalysed by Fe
Contact Process- 2SO2 + O2 —/2SO3 Catalysed by V2O5
Iodide-peroxydisulphate- catalyses by Fe2+

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What is a complex ion?

Central metal ion with one or more ligands bound to it by dative covalent bonds

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What is a ligand?

A molecule or ion that donates a one pair of electrons to a central metal ion via dative covalent bonding

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How do you write a complex ion?

Square brackets around the whole complex
Round brackets for the ligands
Charge on the outside

E.g [Cr(NH3)6] 3+

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What is a coordination number?

The number of dative covalent bonds made to a central metal ion in a complex ion

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What is the shape of a complex with a coordination number of 6? What about 4?

6-Octahedral
4- usually tetrahedral
But if 8 d electron in the ion, becomes square planar
Usually Pt, Au(III) Pd

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What is a monodentate ligand? What is a bidentate ligand?

A ligand which is able to donate 1 lone pair of electrons to a central metal ion, forming 1 coordinate bond e.g ammonia

A ligand which is able to donate 2 lone pairs of electrons to a central metal ion via dative covalent bonding e.g ethanedioate

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When and how is stereoisomerism present in 4 coordinate complexes?

When there no more than 2 identical ligands
Cis/Trans

Same side= Cis, 90 degrees
Opposite side= trans, 180 degrees

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When does Cis/Trans isomerism occur in 6 coordinate complexes?

When two identical ligands and 2 bidentate ligands
Or 4 identical and 2 different

Same monodentate = 90 degrees, Cis
Opposite monodentate= 180 degrees, Trans

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Why do some 6 coordinate complexes have optical isomerism and which do?

Mirror images are not superimposable

In Cis 2 bidentate and 2 monodentate
And 3 bidentate

Draw the mirror image

What is Cis-platin and how does Cis-platin work?

[Pt(NH3)2Cl2]
Anti-cancer drug which inhibits cell division, shrink tumour sizes but lots of side effects
Forms a complex with guanine where the Cls are substituted by the nitrogen’s in the base, prevents DNA replication and triggers apoptosis

What is ligand exchange?

When one ligand is swapped for another

What happens when chromium reacts with dropwise then excess ammonia

Originally Cr3+ Violet
Dropwise- base, hydroxide

Cr3+ + 3OH- —/ Cr(OH)3 (s). Grey green

Excess, full substitution

Cr(OH)3 + 6NH3 —/ [Cr(NH3)6]3+ + 3 OH- Purple

What happens if chromium hydroxide is reacted with excess NaOH?

Grey-Green to Dark Green
Cr(OH)3 + 3OH- —/ [Cr(OH)6]3-

What happens with Cu2+ reacts with dropwise then excess ammonia?

[Cu(H2O)6]2+ pale blue
Dropwise Cu(H2O)6 + 2OH- —/ Cu(OH)2(H2O)4 + 2H2O Blue precipitate
Excess Cu(OH)2(H2O)4 + 4 NH3 —/ [Cu(H2O)2(NH3)4]2+ + 2OH- + 2H2O. Dark Blue solution

Pale blue solution, then blue precipitate, then dark blue solution, partial substitution

What happens when Cu2+ reacts with HCl? Why?

[Cu(H2O)6]2+ + 4Cl- —/ [CuCl4]2- + 6H2O

Pale blue to Yellow
Change in coordination number as the chloride ligands are larger than water, physically not enough space for 6 of them

Why does adding acid enable transition metal hydroxides to dissolve?

Fe2+ + 2OH- /=/ Fe(OH)2

Reversible reaction, adding acid decreases the concentration of hydroxide
Pushes the position of equilibrium to the left, so more ions less precipitate

What is the colour of Fe2+ in solution and it’s hydroxide? Is it soluble in excess hydroxide?

Pale Green solution
Green precipitate
Insoluble

What is the colour of Fe3+ in solution and it’s hydroxide? Is it soluble in excess hydroxide?

Pale yellow solution Orange/brown precipitate Insoluble

What is the colour of Mn2+ in solution and it’s hydroxide? Is it soluble in excess hydroxide?

Pale pink solution Light brown precipitate Insoluble

What is the structure of Haemoglobin?

Metalloprotein Fe2+ with a multidentate haem group coordinated to it 1 space of the globulin protein, and the other for oxygen to coordinate to

What is the function of Haemoglobin? Why is CO toxic?

To transport oxygen around the body Coordination of oxygen creates a weak dative covalent bond, this is a reversible reaction and O2 can disassociate where it is needed by cells for respiration The C of CO forms a much stronger dative covalent bond, substituting for the oxygen, and this is permanent Oxygen can no longer be transported around the body so cells cannot respire, leading to cell death

How do you convert between Fe2+ and Fe3+ including colour changes?

Fe2+= Green Fe3+= orange brown To produce Fe3+, adding an oxidising agent to Fe2+ such as H+/MnO4- To produce Fe2+, adding a reducing agent to Fe3+ such as I-

How do convert between Cr3+ and Cr2O7 2- including colours and intermediates?

Cr3+=Green Cr2O72-= Orange Oxidise Cr3+ by reacting with H2O2/OH-, first forming yellow CrO4 2-, then Cr2O7 2- Reduce Cr2O7 2- with Zn/H+, with excess reducing to form Cr2+ blue

What is the reaction between Cu2+ and Iodide?

2Cu2+ + 4I- —/ 2CuI + I2 White solid and brown solution

What is the reaction between hot Sulphuric acid and Cu2O?

Cu2O+ H2SO4 —/ Cu + CuSO4 + H2O Brown solid and blue solution

What pH is better for reduction and oxidation?

Reduction= acidic Oxidation = alkaline Think about oxidation is the loss of hydrogen and bases remove hydrogens

What shape molecules goes silver form as a complex ion?

Linear, only two ligands

How do transition metals catalyse reactions when homogeneous?

Relies on the variable oxidation states of transition metal ions The ion will take the electron from one molecule and reduce itself It will then oxidise itself by giving the electron to the other reaction Thus catalysing the reaction and regenerating the catalyst Needs an electrode potential between the two reactants