28.1 Physical and chemical properties of first-row transition elements

A transition element is a d-block element that forms one or more stable ions with an incomplete d subshell. The definition concerns ions, not merely the neutral atom’s position in the periodic table.

Check the electron configuration of the common ion. Zinc is d-block but Zn²⁺ is 3d¹⁰, so it is not a transition element under this definition.

Fe²⁺ is 3d⁶ and Fe³⁺ is 3d⁵, so iron qualifies; Sc³⁺ is d⁰ and does not meet the incomplete-d-ion criterion.

“d-block” and “transition element” are not synonyms in every syllabus definition.

The dxy orbital has four lobes lying between the x and y axes in the xy plane. The dz² orbital has two lobes along z with a torus around the centre.

All five d orbitals have the same general four-lobed/axial angular family in an isolated atom, but their orientations differ. In a ligand field, their energies can split.

Sketch axes first, then place dxy lobes between axes and dz² lobes on the z axis with the doughnut in the xy plane.

Do not put dxy lobes on the axes or draw dz² as a simple p orbital.

Partially filled d subshells allow transition elements to access several oxidation states, bond to ligands in complex ions, participate in catalytic cycles and absorb visible light in many compounds.

These are linked but not identical properties: oxidation-state flexibility supports catalysis, ligand-field splitting helps explain colour, and complex formation depends on donor ligands and geometry.

Iron forms Fe²⁺/Fe³⁺, catalyses redox processes, forms [Fe(H₂O)₆]²⁺ and [Fe(SCN)]²⁺, and gives coloured compounds.

Not every d-block ion is coloured or catalytic; d⁰/d¹⁰ configurations and ligand environment matter.

The 3d and 4s subshell energies are close enough that electrons from both can be removed or involved in bonding. This supports multiple stable oxidation states.

The 4s electrons are removed before 3d when forming ions, but once the ion forms the relative energies and ligand environment influence stability. Use actual configurations for the species named.

Fe can form Fe²⁺ ([Ar]3d⁶) and Fe³⁺ ([Ar]3d⁵); both are common because the energy difference is not prohibitive.

Do not say 4s always fills and empties independently of 3d or assume every oxidation state is equally stable.

Transition-metal catalysts can provide alternative pathways because they access multiple oxidation states and have energetically accessible vacant or partially occupied d orbitals that form dative bonds to reactants.

A catalyst may bind, activate and release a substrate, or shuttle electrons between oxidation states. It is regenerated overall and lowers activation energy without changing equilibrium.

Fe²⁺/Fe³⁺ can catalyse a redox chain by accepting an electron in one step and donating it in another.

The catalyst is not consumed permanently, and “vacant d orbital” does not mean every d orbital is empty.

A complex ion contains a central metal ion surrounded by ligands. Empty or energetically accessible orbitals on the metal accept lone pairs to form coordinate (dative) bonds.

The metal charge, size and electron configuration influence ligand binding. Count donor atoms and show the overall charge rather than describing the complex as an ordinary ionic lattice.

[Cu(H₂O)₆]²⁺ forms when six water lone pairs coordinate to Cu²⁺.

A dative bond has both electrons from the ligand but is still a covalent bond once formed; it is not a simple ion pair.