Transition Metals

What is a transition metal?

An element that has an incomplete d sub-level in either the atom or one of the common ions

Give 4 properties of transition metals.

They form complexes

They form coloured ions

Variable oxidation states

Good catalysts

What is a complex?

A molecule consisting of a central metal ion with ligands bonded to it

What is meant by a ligand?

A species that has a lone pair of electrons and can co-ordinately bond to a metal ion

What is a unidentate/monodentate ligand?

A ligand that only forms one coordinate bond with a metal ion

Give some common monodentate ligands.

Cl^-, H₂O,NH₃

What is a bidentate ligand?

A ligand that forms 2 coordinate bonds to a metal ion

Give the names and structures of the 2 required bidentate ligands.

ethane-1,2-diamine

ethanedioate ion

What is a multidentate ligand?

A ligand that forms more than 2 coordinate bonds with a metal ion

Name 2 multidentate ligands.

EDTA and porphyrin

How many co-ordinate bonds does EDTA form?

6

How many co-ordinate bonds does porphyrin form?

4

What is the co-ordination number of a linear complex?

2

What is the bond angle in a linear complex?

180*

When are linear complexes most commonly formed?

In silver (I) complexes

What is the co-ordination number of a square planar complex?

4

What is the bond angle in a square planar complex?

90*

When are square planar complexes formed?

With Pt²⁺ and Ni²⁺ ions

What is the co-ordination number of a tetrahedral complex?

4

What is the bond angle in a tetrahedral complex?

109.5*

When are tetrahedral complexes formed?

With larger ligands like Cl^- ions

What is the co-ordination number in an octahedral complex?

6

What is the bond angle in an octahedral complex?

90*

When are octahedral complexes formed?

With smaller ligands

What is the purpose of haemoglobin?

To transport oxygen around the body

Why is carbon monoxide toxic to humans?

It bonds more strongly to the Fe²⁺ ion in haemoglobin than oxygen, preventing the transport of oxygen around the body

In what complex shapes does cis-trans isomerism occur?

Octahedral and Square planar

Draw the structure of cisplatin.

Draw the structure of transplatin.

Draw the cis and trans isomers of an octahedral complex?

With what complex shape does optical isomerism occur?

Octahedral

When does octahedral isomerism occur in octahedral complexes?

When there are 3 bidentate ligands

Draw 2 optical isomers of an octahedral complex?

How are the d-orbitals arranged in a free transition metal ion?

They are degenerate (have the same energy)

What happens to the d orbitals in a transition metal ion when ligands are attached?

They split so some are at a higher energy than others (normally a 2-3 split)

Explain why we see coloured compounds in transition metal compounds?

Electrons in the lower energy d sub-level absorb light of a specific frequency and are excited

All other frequencies of light are reflected (which we see)

Why is visible light absorbed by d-electrons?

The energy gap between the levels is in the visible light region

Give the equation for the energy absorbed by electrons to excite them.

Energy = h x frequency

Give the value of planck’s constant.

6.63 × 10^-34

What factors effect the colour of a transition metal compound?

The type of metal

The oxidation state of the metal

The ligands

The co-ordination number/ shape of the complex

What is colorimetry?

An analytical technique that uses the absorption of visible light to determine the concentration of a substance (by measuring absorbance)

What is the relationship between concentration and absorption?

They are directly proportional

How can a calibration curve be used to determine the concentration of a unknown substance?

Find the absorption value on the graph and connect to the corresponding concentration

Why do transition metals have variable oxidation states?

They can lose both s and d electrons

Give the 3 main oxidation states of manganese.

MnO₄^- (Mn = +7)

MnO₂ (Mn = +4)

Mn²⁺

In what compound is the manganate ion commonly found?

KMnO₄

What is the standard state of manganese oxide (MnO₂)?

solid

What colour is the Mn²⁺ ion?

colourless

Give some properties of potassium (per) manganate.

Purple liquid

Strong oxidising agent in acidic conditions

Why are most transition metal redox titrations self-indicating?

There is a significant colour change when the metal ion changes oxidation state

Why is H₂SO₄ commonly used to provide the acidic conditions for a redox titration?

It provides sufficient H+ ions and does not react with the reactants or products