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Chemistry · Grades 11–12

Coordination chemistry: an introduction

Read ligands and charge in a simple coordination formula.

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Learn the idea

Complex

A coordination entity has a central atom or ion with surrounding ligands.

Ligand

In the introductory model, a ligand donates an electron pair to form a coordinate bond.

Count

Coordination number counts donor atoms attached to the center, not automatically the number of written ligand formulas.

Charge

Combine the metal oxidation state and ligand charges to obtain the charge of the complex.

Worked examples

What is a ligand in an introductory coordination model?

A ligand provides a donor atom and an electron pair.

An electron-pair donor bonded to a center.

In [Cu(H₂O)₆]²⁺, each water is neutral. What is copper’s oxidation state?

Neutral ligands leave the +2 complex charge on the metal accounting.

2

Check your understanding

  1. In [Co(NH₃)₆]³⁺, each ammonia binds through one donor atom. What is the coordination number?

  2. In [Fe(CN)₆]⁴⁻, each CN ligand is −1. What is iron’s oxidation state?

  3. Can a ligand bind through more than one donor atom?

    1. Only if the metal has no electrons.
    2. No, by definition all ligands bind once.
    3. Yes; such ligands can be multidentate.

Answers and marking notes

Answers and marking notes
  1. 6

    Six singly attached donor atoms surround the metal.

  2. 2

    x − 6 = −4 gives x = +2.

  3. Yes; such ligands can be multidentate.

    Dentate describes the number of donor sites used by a ligand.

Further reading and review references

These are reference links, not copied exercises, institutional endorsement or proof of independent review.

Independent educational review required. Grade bands are approximate; these are not officially aligned curricula.