28.2 General Characteristic Chemical Properties of the First Set of Transition Elements: Titanium to Copper

2026 Syllabus Objectives

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

  1. Describe and explain how transition elements react with ligands to form complexes, including the complexes of copper(II) and cobalt(II) ions with water, ammonia, hydroxide, and chloride.
  2. Define the term ligand.
  3. Understand and use the terms monodentate, bidentate, and polydentate ligand, with examples.
  4. Define the term complex.
  5. Describe the geometry (shape and bond angles) of linear, square planar, tetrahedral, and octahedral complexes.
  6. State what is meant by coordination number, and predict the formula and charge of a complex ion.
  7. Explain qualitatively how ligand exchange occurs in copper(II) and cobalt(II) complexes.
  8. Predict, using E⦵ values, whether a redox reaction involving transition elements is feasible.
  9. Describe and perform calculations for the redox systems: MnO₄⁻/C₂O₄²⁻, MnO₄⁻/Fe²⁺, and Cu²⁺/I⁻.
  10. Perform calculations involving other redox systems given suitable data.

Section 1: What is a Complex?

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A complex (also called a coordination compound) is a molecule or ion made up of a central metal atom or ion surrounded by one or more ligands.

  • The central metal is almost always a transition metal ion (e.g. Cu²⁺, Co²⁺, Fe²⁺, Fe³⁺).
  • The ligands are bonded to the metal by a special type of bond called a dative covalent bond (also called a coordinate bond).

What is a Dative Covalent Bond?

In an ordinary covalent bond, both atoms contribute one electron each to the shared pair. In a dative covalent bond, both electrons in the bond come from one atom — the ligand donates both electrons to the metal. The metal simply accepts the pair.

Section 2: What is a Ligand?

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A ligand is a molecule or ion that:

  • Contains at least one lone pair of electrons (a pair of electrons not involved in bonding within the ligand itself), and
  • Donates that lone pair to a central metal atom or ion to form a dative covalent bond.

In plain English: A ligand is like a "donor" — it grabs onto the metal by offering a pair of electrons.

Types of Ligands

Ligands are classified by how many dative bonds they can form with the central metal:

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