28.1 General Physical and Chemical Properties of the First Row of Transition Elements, Titanium to Copper

2026 Syllabus Objectives

By the end of these notes, you should be able to:

  1. Define a transition element as a d-block element which forms one or more stable ions with incomplete d orbitals
  2. Sketch the shape of a 3dxy_{xy} orbital and a 3dz2_{z^2} orbital
  3. Understand that transition elements have the following properties:
    • (a) Variable oxidation states
    • (b) They behave as catalysts
    • (c) They form complex ions
    • (d) They form coloured compounds
  4. Explain why transition elements have variable oxidation states in terms of the similarity in energy of the 3d and 4s sub-shells
  5. Explain why transition elements behave as catalysts in terms of having more than one stable oxidation state, and vacant d orbitals that are energetically accessible and can form dative bonds with ligands
  6. Explain why transition elements form complex ions in terms of vacant d orbitals that are energetically accessible

1. What Is a Transition Element?

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The Definition

A transition element is a d-block element that forms one or more stable ions with incomplete (partially filled) d orbitals.

Let's break that down:

  • d-block element — These are elements found in the middle section of the Periodic Table, sitting between Group 2 on the left and Group 13 on the right. They are all metals.
  • d orbital — A type of atomic orbital (region where electrons are found). There are five d orbitals in the 3d sub-shell, and together they can hold a maximum of 10 electrons.
  • Incomplete d orbitals — This means the d sub-shell is neither completely empty (0 electrons) nor completely full (10 electrons) in the ion the element forms.

The first row of transition elements goes from titanium (Ti) to copper (Cu), and all of them sit in Period 4 of the Periodic Table.

Why Scandium and Zinc Are NOT Transition Elements

Even though scandium (Sc) and zinc (Zn) are in the d-block, they are not classed as transition elements:

  • Scandium (Sc) only forms one ion: Sc³⁺. When it loses 3 electrons, its 3d sub-shell is completely empty (0 electrons). An empty d sub-shell is not an incomplete d sub-shell — it's simply empty. So Sc does not meet the definition.

  • Zinc (Zn) only forms one ion: Zn²⁺. When it loses 2 electrons, its 3d sub-shell is completely full (10 electrons). A full d sub-shell is also not incomplete. So Zn does not meet the definition either.

💡 Key point: The definition specifically says the ion must have an incomplete d sub-shell — not the atom itself. Always think about the ion, not the neutral atom.

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