IB CHEMISTY HL

13.2- First row b-block

Elements

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13.2

Transition metals characteristic properties

Electron configuration

• Similarity in 1𝑠𝑡 row d- bloc elements properties are shown by the small

range in atomic radii-

𝑆𝑐 [𝐴𝑟] 3𝑑1 4𝑠2

𝑇𝑖 [𝐴𝑟]3𝑑2 4𝑠2

𝑉 [𝐴𝑟]3𝑑3 4𝑠2 𝑉3 + [𝐴𝑟]3𝑑2

𝐶𝑟 [𝐴𝑟]3𝑑5 4𝑠1

𝑀𝑛 [𝐴𝑟]3𝑑5 4𝑠2

𝐹𝑒 [𝐴𝑟]3𝑑6 4𝑠2

𝐶𝑜 [𝐴𝑟]3𝑑7 4𝑠2 𝐶𝑜2 + [𝐴𝑟]3𝑑7

𝑁𝑖 [𝐴𝑟]3𝑑8 4𝑠2

𝐶𝑢 [𝐴𝑟]3𝑑10 4𝑠1

𝑍𝑛 [𝐴𝑟]3𝑑10 4𝑠2

When d block elements form ions, the 4𝑠 electrons are lost first

13.2.2 Transition metals

A transition metal is one which forms one or more stable ions which have

incompletely filled and orbitals.

Not all d block elements count as transition metals → scandium and zinc are not

transition metals

Variable oxidation state (Number)

One of the key features of transition metals is its wide range of oxidation states

(number) the metals can show.

Oxidation state / Number → the number of electrons lost, gained or shared as a

result of chemical bonding.

• Oxidation → increase in oxidation state (loss of electrons)

• Reduction → decrease in oxidation state (gain of electrons)

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Assigning oxidation Numbers

E.g. Write down the oxidation number for the metal

C𝑟2𝑂72− [𝐹𝑒(𝐻2𝑂)6]3+

2𝑥 + (−2 × 7) = −2 𝑥 + (1 × 12) + (−2 × 6) = 3 +

2𝑥 − 14 = −2 𝑥 + 12 − 12 = 3 +

2𝑥 = 12 𝑥 = 3 +

𝑥 = 6 𝐹𝑒3+

𝐶𝑟26+

Because it’s increase in successive energies is more gradual (3𝑑 and 4𝑠 orbitals are

close in energy level) because the large jump occurs between the 4th and 5th

ionisation energies. It does not form a +5 state

𝑆𝑐 𝑇𝑖 𝑉 𝐶𝑟 𝑀𝑛 𝐹𝑒 𝐶𝑜 𝑁𝑖 𝐶𝑢 𝑍𝑛

+1

+2 +2 +2 +2 +2 +2 +2 +2 +2

+3 +3 +3 +3 +3 +3 +3 +3 +3

+4 +4 +4 +4 +4 +4 +4

+5 +5 +5 +5 +5

+6 +6 +6

+7

Transition motels can show a variation of oxidation numbers because the 3d and

4s orbitals are very similar in energy so their successive ionisation energies is very

gradual.

• All transition metals show both +2 and +3 oxidation states

• The 𝑀3+ ion is the stable for elements form 𝑆𝑐 to 𝐶𝑟. The 𝑀2+ state is more

common for later elements (Because the increased nuclear charge of later

elements makes it more difficult to remove the 3𝑟𝑑 electron)

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• The max. oxidation state of the elements increases in steps of +1 and

reaches a maximum at manganese. Thereafter, the max oxidation state

decreases in steps of −1

• Oxidation states above +3 generally show covalent character.

• Compounds with higher oxidation states tend to be oxidising agents.

Complexes (13.2.5)

Ligands

A complex ion has a metal ion at its centre with a number of other molecules or

ions surrounding it. These are attached to the central ion by coordinate (dative

covalent) bonds.

The molecules or ions surrounding the central metal ion are called ligands.

Simple ligands include water, ammonia and chloride ions.

These all have active lone pairs of electrons in the outer energy level – These are

used to form coordinate bonds with the metal ion.

Example of ligands

𝐻2𝑂, 𝑂𝐻−, 𝐶𝑙−, 𝑁𝐻3 , 𝐶𝑁−

A ligand is a species that uses a lone pair of electrons to form a dative covalent

bond with a metal ion.

Transition metal ions can form complex ions because. Its relatively high charge

and small size which allow them to attract the lagan’s lone pairs of electrons.

Shapes of some complex ions

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In aqueous solution, water molecules generally act as ligands, but these can be

replaced in a process calld ligand exchange.

Example of complex ion : 𝐴𝑙3+ ( when added to water)

• 𝐴𝑙3+ has a high charge density and a small logic radius, which attracts the

water molecules.

• The water molecules form a dative covalent bond with long to form an

octahedral complex ion. [𝐴𝑙(𝐻2𝑂)6]3+

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• A complex is formed when a central ion is surrounded by molecules or ions

which have a lone pair of electrons.

• A dative covalent (coordinate) bond uses a lone pair of electrons to form a

covalent bond.

The hydrated ion is acidic as the high charge density of the 𝐴𝑙3 + ion attracts the

electrons of the 𝑂 − 𝐻 bond. And releases an 𝐻+ ion to form an acidic solution.

[𝐴𝑙(𝐻2𝑂)6]3+(𝑎𝑞) ⇌ [𝐴l(𝐻2𝑂)5𝑂𝐻]2+(𝑎𝑞) + 𝐻+(𝑎𝑞)

13.2.6. Explain why some complexes of d – block elements are coloured

The colour of transition metal ion complexes

The colour of transition metals are due to the movement of unpaired electrons

between split d – orbitals.

When a metal ion forms a complex, the 𝛼 orbitals are split into 2 distinct energy

levels. (when electrons)

Are excited and move between these split 𝛼 orbitals. They absorb a particular

frequency of light energy transmitting a colour complementary to this.

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Different ligands cause different amounts of splitting therefore different

complexes have different colours.

𝑍𝑛2 + has a full 𝛼 orbital and 𝑆𝑐3 + has an empty 𝛼 orbital → therefore these compounds

are colourless These are only colours when these are unpaired 𝛼 electrons.

(the d-orbitals in a transition metal atom are degenerate – all have the same

energy)

The amount the orbitals are split depends on

• The nuclear charge of central metal ion

• The charge density of ligand

• The oxidation number of the central ion

• The shape of the complex ion

The d – orbitals split 2 sub – levels when a metal ion forms a complex because of

the electric field produced by the ligand’s lone pair of electrons.

13.2.7 State examples of the catalytic action of transition elements and their

compounds

Transition Metals as Catalysts

Catalysts speed up chemical reactions by providing an alternative pathway of

lower activation energy.

Transition metals are effective catalysts due to

• Their ability to form more than one stable oxidation state. (homogenous)

• Their ability to allow reactants to adsorb onto their surface and activate

them in the process (heterogenous)

Heterogenous catalysts

• The catalyst is in a different state than the reactants.

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• Transition metals use the 3d and 4s electrons to form weak bonds to small

reactant molecules which provides a surface for the reactant molecules to

come together.

Examples

Iron (𝐹𝑒) Haber process 𝑁2(𝑔) + 3𝐻2(𝑔) ⇌ 2𝑁𝐻3(𝑔)

Nickel (𝑁𝑖) Conversion of alkenes to alkanes catalytic

converters

Palladium (𝑝𝑑)/ platinum (𝑃𝑡)

𝑀𝑛𝑂2 Decomposition of hydrogen peroxide

𝑉2𝑂5

Vanadium (v) oxide

Contact process

Heterogenous catalysts is preferred in the industrial processes because it can be

easily removed by filtration after use.

Homogenous Catalysts

• Same state as the reactants.

• Vatable oxidation states allow them to be effective in REDOX reactions

Examples:

• 𝐹𝑒2+ → Heme (reaction of 𝐻2𝑂2 with iodide ions

• 𝐶𝑜3+ → Vitamin B

• Chlorine atoms → catalyse the breakdown of ozone (𝑂3)

(13.2.8) outline the significance of catalysts in the contact and Haber processes.

Contact process

2𝑆𝑂2 (𝑔) + 𝑂2 (𝑔) ⇌ 2𝑆𝑂3(𝑔)

𝑉2𝑂5 (Vanadium (V) oxide) → catalyst

Sulphur trioxide (𝑆𝑂3) is used in the manufacture of sulfuric acid → manaufacturing

world’s most important chemical.

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Haber process

𝑁2(𝑔) + 3𝐻2(𝑔) ⇌ 2𝑁𝐻3(g)

Iron (𝐹𝑒) → Catalyst

Ammonia is the raw material for a large number of other useful chemical products

such as fertilisers, plastics, drugs and explosives.

Characteristic properties of transition metal’s

• Form compound in which the element exists in variable oxidation states.

• Tend to have higher melting points and are harder and denser than group

1 and 2 metals

• Catalytic properties

• Majority of their compounds are coloured