Typical Properties of Transition Metals

General Characteristics

Transition metals are known for being hard and dense metals. They have high melting points, which means they remain solid at temperatures where many other metals would melt. This is because of the strong metallic bonds formed by their atoms. The presence of d-electrons in transition metals contributes to these strong metallic bonds, making them harder and giving them higher melting points compared to other metals.

They are excellent conductors of heat and electricity due to the presence of delocalised electrons that can move freely through the metal lattice. Their high tensile strength means they can withstand stretching forces without breaking, making them useful in construction and manufacturing.

For example, iron is much harder and denser than alkali metals like sodium, and it melts at a much higher temperature (iron melts at 1538°C).

Variable Oxidation States

One of the key features of transition metals is their ability to exhibit multiple oxidation states. Unlike Group 1 metals, which typically form only +1 ions, transition metals can form ions with different charges, commonly +2 and +3.

This happens because their d-sublevel electrons can be lost or shared in reactions, allowing for a variety of oxidation states. For example, iron can form Fe²⁺ and Fe³⁺ ions.

Transition metals often form coloured compounds due to the way their d-electrons absorb and emit light. For instance, copper(II) sulfate solution is blue, and chromium compounds can be green or purple.

They also have the ability to form complex ions, where the metal ion is surrounded by molecules or ions called ligands. Ligands are molecules or ions that donate electron pairs to the metal ion to form these complex ions. This property is important in many biological and industrial processes.

For example, the complex ion $[Cu(H_2O)_6]^{2+}$ is blue in solution.

For instance, iron(III) chloride forms the complex ion $[FeCl_4]^ -$, showing iron in the +3 oxidation state.

Example: Iron can form Fe²⁺ and Fe³⁺ ions. The Fe²⁺ ion forms pale green compounds, while Fe³⁺ forms brown compounds.

Catalytic Properties

Transition metals and their compounds are widely used as catalysts in industry. Catalysts speed up chemical reactions without being used up themselves.

The surface atoms of transition metals can adsorb reactant molecules, weakening bonds and making reactions easier.

Examples include:

• Iron used as a catalyst in the Haber process to produce ammonia from nitrogen and hydrogen.
• Nickel used as a catalyst in hydrogenation reactions, such as converting vegetable oils into margarine.

These catalytic properties are linked to their ability to change oxidation states and form temporary bonds with reactants.

Magnetic and Physical Properties

Some transition metals are magnetic. For example, iron, cobalt, and nickel are ferromagnetic, meaning they can be permanently magnetised.

Transition metals generally have high density and strength, making them suitable for structural uses.

They are also malleable and ductile, meaning they can be hammered into sheets or drawn into wires without breaking.

This combination of strength, density, and malleability is why transition metals are widely used in engineering and construction.

For instance, calculating density is important in understanding physical properties. For example, if a sample has a mass of 500 g and a volume of 62.5 cm³, its density is calculated as:

Density $= \frac{\text{mass}}{\text{volume}} = \frac{500 \text{ g}}{62.5 \text{ cm}^3} = 8 \text{ g/cm}^3$