Transition Elements

Section: General Characteristics of Transition Elements

  • Transition elements are found in the middle block (groups 3-12) of the Periodic Table.
  • They have variable oxidation states, meaning they can exist in two or more stable states.
  • All transition elements are metals, having similar properties like high melting points and good conductivity of heat and electricity.

Section: Electronic Configuration

  • Transition elements have an outer electronic configuration of 4s^2 3d^n, where n varies from 1 to 10.
  • During ionisation, the 4s electrons are lost first, despite being filled later than the 3d subshell. This surprising behaviour is attributable to the 4s electrons having a higher energy level once the atom is neutral and the 3d subshell starts filling up.

Section: Variable Oxidation States

  • The variable oxidation states in transition elements are due to the participation of both s and d electrons in bonding.
  • The energy difference between 4s and 3d electrons is small, hence both can participate in bonding, leading to variable oxidation numbers.
  • The oxidation state can vary from +1 to +7 depending on the electron configuration and the specific element.

Section: Colour and Transition Elements

  • Many transition metals and their compounds are coloured. This is the result of electron transitions between the 3d and 4s energy levels when light hits the metal atom.
  • Different colours arise due to the different energy gaps between these energy levels in different elements or ions.

Section: Formation of Complex Ions

  • Transition elements can form complex ions. These are ions with a central metal atom or ion, surrounded by one or more atoms, ions or molecules known as ligands.
  • They form coordination compounds with suitable ligands due to the presence of empty d-orbitals that can accept pairs of electrons from electron-rich species (ligands).

Section: Catalysts

  • Many transition elements and their compounds act as catalysts. This is because they can easily change their oxidation states (an important process in most catalytic reactions) and form complex compounds.
  • For example, nickel (Ni) is used in the hydrogenation of alkenes, and iron (Fe) is used in the Haber process for the manufacturing of ammonia.