13.2 - First-Row D-Block Elements

13.2 - First-Row d-Block Elements

13.2.1 - List the characteristic properties of transition elements 

A variable oxidation number

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Higher melting points, harder and denser than group 1 and 2 metals

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Form complex ions

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Majority of their compounds are coloured

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Can act as catalysts

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No significant change in atomic radii due to repulsion between the 4s and 3d electrons

13.2.2 - Explain why Sc and Zn are not considered to be transition elements Scandium and Zinc do not have a partially filled d subshell. Since the ions do not have a partially filled d subshell, they are not considered to be transition metals. They only have one possible oxidation state, while all transition metals have variable oxidation states.

13.2.3 - Explain the existence of variable oxidation number in ions of transition elements Cr Mn Fe Cu

2+ 2+ 2+ 1+

3+ 6+ 4+ 7+ 3+ 2+

The maximum oxidation number possible for titanium to manganese is equal to the number of electrons in the 4s and 3d subshells Electrons are lost form both the 4s and 3d subshells because their energy levels are so close

13.2.4 - Define the term ligand An ion or small polar molecule that is attracted to the transition metal ions because it has an electron pair that it can donate to the central metal ion. Examples: NH3 CO Cl- CN- OH- H2O

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13.2.5 - Describe and explain the formation of complexes of d-block elements Transition metal ions are highly charged and strongly attract ions and polar molecules. As a result, they can form a complex ion, linked by coordinate (dative) bonds. There are typically two to six ligands surround a transition metal in a complex. The coordination number is the number of ligands surrounding the central ion. The name of the complex indicates the type and number of ligands. The number of ligands affects shape of the complex.

13.2.6 - Explain why some complexes of d-block elements are coloured When transition metal complexes are placed in light, parts of white light are absorbed, and the complementary colours are seen. Orbitals of complex ions are split into two levels. The closer a ligand can get to the ion, the larger the split of the d-orbital. The splitting depends on: 

The charge on the transition metal ion, as higher charge has greater pull on the ligands, creating a larger split

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The size of the ligand, since smaller ligands can get closer to the ion, increasing the split size according to:

Light falling on the complex causes electrons at lower energy levels to be excited. They move to a higher energy level, absorbing light. The difference in the split of the energy levels determines the wavelengths of energy that is absorbed. Different ligands also form different colours If a transition metal does not have any d-orbital electrons, or the d-orbitals are full, then the ion will be colourless. Complexes can still form.

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13.2.7 - State examples of the catalytic action of transition metals and their compounds MnO2 This is used as a catalyst for the decomposition of H2O2, hydrogen peroxide V2O5 Pellets are used in the Contact process to make H2SO4 Fe Porous iron is used in the Haber process to make NH3. Also found in heme, and binds to oxygen to transport it in the blood. Ni Used in hydrogenation to convert alkenes to alkanes, such as in the production of margarine Co This is found in vitamin B12 and aids the production of red blood cells and the functioning of the nervous system Pd and Pt Used in the decomposition CO, NO and NO2 in the catalytic converter of car exhausts.

13.2.8 - Outline the economic significance of catalysts in the Contact and Haber processes Contact Process - Used to produce Sulfuric Acid Sulfuric acid is used for: 

Fertilisers

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Paints

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Pigments and dyes

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Manufacturing other chemical compounds

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Soaps and detergents

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Fibres

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Plastics

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Processing metals

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Heterogeneous catalysts are when the catalyst is in a different state to the reactants Pellets of vanadium oxide (V2O5) as a solid catalyst are employed. Using the catalyst overcomes disadvantage of to use lower than ideal temperatures to produce satisfactory yields at equilibrium. The oxidation state of the transition metal changes during the reaction, then is regenerated at the end.

This equilibrium is an exothermic reaction, hence favoured by low temperatures and high pressures. Low temperatures cause slow reaction, so catalyst is needed. A faster reaction makes it economically viable

Haber Process - Used to produce Ammonia Ammonia is used for: 

Fertilisers

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Nylon

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Manufacturing other chemical compounds

Porous from of iron and potassium hydroxide is used for the reaction. Other transition metals could be used, however these are more expensive. Without the catalyst, the reaction would not be economically viable

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