2.4 - Transition Metals

Give 2 properties of Transition Metals

1. Transition metals occupy the d-block

2. Catalytic

Give 2 examples of Transition metals acting as a Catalyst

1. Platinum in fuel cell

2. Nickel in nitrile reduction to amines

What are the colours of CuSO₄ in different states? (when light shines on it)

• Why

• Solid = White

• Liquid = Cyan

Red light is absorbed so the complimentary colours show

How do we see a compound’s colour when light is cast on it?

Lights different wavelength of light shows the corresponding colours which have the exact amount of energy to excite electrons to the next orbital (given it has space for it)

What is the usual order of Subshells for Transition Metals?

• 2 anomalies + configuration (why)

3d 4s:

• Cr = [Ar] 4s¹3d⁵ → 3d is half filled to similar energy level to 4s, so the electron occupies it

• Cu = [Ar] 4s¹3d¹⁰

What does this effect in terms of ionisation?

When being ionised for Cu + Cr, the 4s s lost first or gains the electron

Why do Transition metals form coloured compounds?

• Range of metals

Transition metals are the only ions that are stable, whilst having partially filled d-orbitals → excitation of electrons to the partially filled orbitals and their de-excitation gives colour:

• Ti → Cu

Complex Ions

Complex Ions

What is a Ligand? (3 examples)

A particle with a lone pair that datively covalently bonds to a transition metal ion:

• H₂Ö

• N̈H₃

• :Cl^-

Why do Complex Ions with the same Metal have different co-ordinate numbers?

Ligands, for example Cl, are greater in size than other ligands, like NH₃, can only occupy space as a tetrahedral

What is the priority for a Complex Ions when writing general formula?

• Example = Amino,aqua,di-chloro platinum (II)

1. Neutral

2. Positive

3. Negative

• [Pt(NH₃)(H₂O)(Cl)₂]⁰

Name the following Complex ions:

1. [V(H₂O)₆]³⁺

2. [Co(NH₃)₆]²⁺

3. [Co(Cl)₄]^2-

4. [Co(H₂O)₃(NH₃)₃]²⁺

1. Hexa Aqua Vanadium(III)

2. Hexa Ammine Cobalt (II)

3. Tetra Chloro Cobaltate (II)  → “-ate” for negative complex ions

4. Triammine,Triaqua Cobalt (II)

Which 3 metals have Square Planar complex ions - no matter what ligands are attached to them?

• What are the shapes of the rest

Platinum, Nickel, Palladium:

• All other metals have Octahedral shapes → square planar for large ligands 

When is a Square Planar complex ion:

• Cis

• Trans

• Cis = When identical ligands are on the same side (Left or right)

• Trans = When identical ligands are on the opposite side

When is Transplatin used?

Trans platin is more stable than Cisplatin, so it’s used when transporting → then it is converted to Cisplatin for cancer treatment

When is an Octahedral Complex ion:

• Cis

• Trans

• Cis = When identical ligands are 90^o from eachother (basically when 2 identical ligands are separated by one different ligand)

• Trans = When identical ligands are on opposite sides of eachother

What is:

• Polychromatic light

• Monochromatic light

• Polychromatic light = Contains mixture of wavelengths of light of different colours

• Monochromatic light = Contains one wavelength of light of the same colour

What are the gaps between orbitals equivalent to?

Frequency of light needed to excite electrons

Why are most compounds colourless?

Most compounds energy level split is too larger so light doesn’t hold enough energy to excite electrons

Why do Complex ions form coloured compounds?

When ligands datively covalently bond to ions, the metal ions d-orbitals split equally. The gap is small so wavelengths of light that are shone onto a sample can excite electrons from the lower half of the orbital to the upper half, when electrons de-excite they emit wavelengths of light with a corresponding colour

Why do few Complex ions not form coloured compounds?

• Example of a metal that doesn’t

When the d-orbital is full, there is no space for a lower electron to excite + occupy the orbital, so when light is shone, no colour is transmitted:

• Zinc

What is the relationship between Energy level gap of orbitals and frequency?

• Include in terms of colour

Direct proportion:

• Higher frequency = Blue-er

• Lower frequency = Redd-er

What are the 2 formulae for the Energy between orbitals?

1. E = hf

2. E = hc/λ

• h → planck’s constant = 6.63 × 10^-34

What is the relationship of Oxidation state and Frequency?

• (+ colour observed)

Direct proportion = As oxidation number increases, it absorbs a larger frequency of light:

• Colour observed is less blue

(vice versa)

Order the following ligands in terms of D-Orbital splitting, Absorbed Frequency, Energy gap between orbitals, Colour:

• NH₃

• H₂O

• Cl

> D - Splitting / Frequency + Energy change (increasing):

• Cl, H₂O, NH₃

> Colour (how blue it is):

• NH₃, H₂O, Cl

Order the following Co-ordination numbers in terms of D-Orbital splitting, Energy gap between orbitals, Colour:

• Octahedral (C.No = 6)

• Square Planar (C.No = 4)

• Tetrahedral (C.No = 4)

> D - Splitting / Frequency + Energy change (increasing):

• Tetrahedral, Square Planar, Octahedral

> Colour (how blue it is):

• Octahedral, Square Planar, Tetrahedral

Explain the effect of Complex ion’s shape on its colour?

• What is the additonal factor

Ligands effects the geometry of molecules so effect the ions D-splitting:

• Type of metal ion

Colorimetry

Colorimetry

What is Colorimetry?

• 2 advantages

Use of light source + colour filter, shining the light at the sample with a complimenting colour to the light, then measuring the amount of light absorbed by the solution:

1. Quick process

2. Doesn’t require large sample

Give the 3 step method to carry out Colorimetry

1. We compare our sample absorption to know concentration + their absorption

2. Plot a graph of these values

3. Extrapolate the absorption from STEP 1 to the graph to find the corresponding concentration

What are the axis’ for a Calibration curve?

• x-axis = Concentration

• y-axis = Absorption

Why is their a plateau on Calibration curve?

Absorption not proportional to concentration

What is Complete ligand substitution?

Where all ligands are replaced

What is Incomplete ligand substitution?

Where a few ligands are replaced

What are the products of:

• [Co(H₂O)₆]²⁺ + 4Cl^-

• Why is this?

• Entropy of this reaction

[Co(H₂O)₆]²⁺ + 4Cl^- → [Co(Cl)₄]^2- + 6H₂O

• Cl is too large so can replace all 6 water ligands with 4 Cl

• High entropy since more products than reactants

What is a Bidentate Ligand? (co-ordinate number)

Singular Ligands that form 2 dative covalent bonds to a complex ion:

• 1 bidentate ligand = 2 co-ordinate number

What is prefix for the following Complex ions:

• 2 bidentates

• 3 bidentates

• 4 bidentates

1. 2 bidentates = Bis

2. 3 bidentates = Tris

3. 4 bidentates = Tetrakis

What is the structure of the “en” ligand?

• Type of ligand

• Charge

C₂H₄(NH₂)₂

• Bidentate

• Charge = 0

What is the structure of the Oxylate ligand?

• Type of ligand

• Charge

C₂O₄^2-

• Bidentate

• Charge = -2

What type of Isomerism do Complex ions observe?

• Exceptions

Optical Isomers → enantiomers of eachother:

• Linear/Square planar ions

What is the Chelate effect?

The replacement of monodentate ligands to multidentate ligands, such that entropy increases

Comment + Explain on the following about the Chelate effect:

• Entropy

• Feasibility

Entropy increases as the number of reactants < products. So entropy of forward reaction is high - meaning reaction is likely to occur + since enthalpy = 0 → reaction is always feasible

What is EDTA?

• Number of lone pairs, atoms and charge

• Entropy → its effect

A multidentate ligands with:

• 4O:^- and 2N: so one EDTA replaces 6 ligands, -4 charge 

• High entropy of 2 reactants to 7 products → quickly reacts

What is the use of EDTA? (explain)

Prevention of lead poisoning in body, large entropy so feast reaction which quickly halts the effect of Pb poison in the body by forming harmless complex ions with Pb

What is Haem?

• Describe structure

• Bonds formed

• What is bonds with

Haem is an Fe(II) complex with multidentate ligand that can form 4 dative covalent bonds:

• Bonds with protein globin

• Forms Haemoglobin complex

What does the Haemoglobin complex can do? (use)

Forms co-ordinate bonds with O₂ + H₂O ligands which are easily formed + broken:

• Respiration

Explain how Haemoglobin work with Oxygen, Water and Carbon Dioxide

Haem forms weak co-ordinate bonds with oxygen, water and carbon dioxide so easily transports to + from muscles. Don’t form stable bonds with Fe²⁺

Explain how CO poisoning with Haemoglobin occur

CO forms stable bonds w/ Haem so decreased number of useable Haem for respiration meaning no Oxygen absorption, and increased Carbon Dioxide + CO in blood leading to death