Resources | Subject Notes | Chemistry
Transition elements are defined by having an incomplete d-orbital. This characteristic leads to a range of interesting and often variable chemical properties. This section will cover their general properties, reactions, variable oxidation states, and complex formation.
Metallic Character: Transition metals are typically metals, exhibiting metallic properties such as luster, conductivity, and malleability. However, their metallic character can vary significantly within a series.
High Melting and Boiling Points: Transition metals generally have high melting and boiling points due to the presence of delocalised electrons and strong metallic bonding.
High Density: They are generally dense metals.
Formation of coloured compounds: Many transition metal compounds are coloured, arising from d-d electronic transitions.
Variable Oxidation States: A key characteristic of transition elements is their ability to exhibit multiple oxidation states. This is due to the small energy difference between the (n-1)d and ns orbitals, allowing electrons to be lost from either orbital.
Transition metals react with oxygen at high temperatures to form oxides. The oxides can be either coloured or colourless, depending on the metal and the oxidation state of the metal.
Transition metals react with halogens, often forming complex halides. The stoichiometry of the reaction can be complex, often involving the formation of intermediate species.
Transition metals generally react with acids to form salts and hydrogen gas. The reactivity varies depending on the metal and the acid.
Transition metals exhibit variable oxidation states, which are the different charges a metal can have in a compound. The common oxidation states are often related to the number of d-electrons present.
For example, Iron (Fe) can exhibit oxidation states of +2, +3, and +4.
The ability to have multiple oxidation states is crucial for the formation of complex ions and the catalytic properties of transition metals.
| Transition Metal | Common Oxidation States |
|---|---|
| Iron (Fe) | +2, +3, +4 |
| Copper (Cu) | +1, +2 |
| Nickel (Ni) | +2, +3 |
| Manganese (Mn) | +2, +3, +4, +6 |
Transition metals have a strong tendency to form complexes with ligands. A ligand is a molecule or ion that donates a pair of electrons to the metal ion, forming a coordinate covalent bond.
Ligands can be classified as neutral (e.g., ammonia, water), anionic (e.g., chloride, cyanide), or cationic (e.g., ammonium).
The coordination number is the number of ligands directly attached to the central metal ion. Common coordination numbers are 4 and 6.
Coordination Complexes: These are formed when ligands donate electron pairs to the metal ion. The metal ion acts as a Lewis acid, and the ligands act as Lewis bases.
Formation of coloured complexes: The colour of transition metal complexes arises from d-d electronic transitions. The energy of the transition corresponds to the colour observed.
Isomerism: Coordination complexes can exhibit isomerism, which is the existence of isomers with the same molecular formula but different arrangements of atoms. Types of isomerism include:
Crystal Field Theory (CFT) and Ligand Field Theory (LFT): These theories are used to explain the electronic structure and properties of transition metal complexes. They predict the colour and magnetic properties of complexes.