Ch 9Coordination Compounds — Class 12 Chemistry, concept-first.

A coordination compound consists of a central metal atom or ion surrounded by ions or molecules called ligands.

Ligands are classified according to how many donor atoms they use to bind a single central metal ion. A monodentate ligand offers just one donor atom and therefore forms only one coordinate bond to th…

A monodentate ligand has a single donor atom, and that one atom shares one electron pair to form exactly one coordinate bond with the central metal ion.

A polydentate ligand has two or more donor atoms, all of which link simultaneously to the SAME central metal ion (this multi-point attachment is called chelation, and the resulting ring-shaped structu…

An ambidentate ligand genuinely possesses two different donor atoms, but forms a coordinate bond through only ONE of them at a time in any given complex -- the two possible binding modes give rise to…

This section defines the core working vocabulary used to describe and analyse coordination compounds throughout the rest of the chapter: the coordination sphere and the counter ions outside it (9.3.1)…

The coordination sphere is the central metal ion together with all the ligands directly bonded to it, conventionally enclosed together in square brackets -- it behaves as one discrete structural unit.…

The charge number of a complex ion is simply its net overall charge -- the algebraic sum of the oxidation state (charge) of the central metal ion and the total charge contributed by all its ligands to…

The coordination number (C.N.) of the central metal ion in a complex is the number of ligand DONOR ATOMS directly attached to it -- equivalently, the number of coordinate bonds (electron pairs) it is…

Combining two or more separately stable compounds in a fixed stoichiometric ratio can give rise to two structurally different kinds of substance: a double salt or a coordination complex, and telling t…

Werner made the first serious attempt to explain how bonding works in coordination compounds, and his theory rests on four postulates.

Coordination complexes can be classified along two entirely independent axes. The first axis looks at the TYPES of ligands present in the coordination sphere -- whether a complex contains just one kin…

A homoleptic complex has its central metal ion bound to only ONE type of ligand. [Co(NH3)6]3+ is the book's example: every one of the six ligands around cobalt is NH3, and nothing else.

A cationic complex has a positively charged coordination sphere -- either the whole compound is simply that cation (e.g.

IUPAC lays down a fixed set of rules for naming coordination compounds unambiguously. Rule 1: name the ligand(s) first, and only then the central metal.

The Effective Atomic Number (EAN) rule was an early attempt, proposed by Sidgwick, to explain why some coordination compounds are especially stable.

Isomers are different compounds that share exactly the same molecular formula but differ in their chemical reactivity and in physical properties such as colour, solubility, and melting point.

Stereoisomers share identical bonding connectivity but differ in spatial arrangement, and coordination chemistry recognises two kinds.

Structural (constitutional) isomers have genuinely different atom-to-atom linkages, even though their overall chemical formula is identical, and this chapter recognises four distinct sub-types.

The stability of a coordination compound reflects how strongly its metal-ligand interactions hold it together, and this can be measured quantitatively through the complex's stability (formation) const…

Two distinct factors govern how stable a given coordination complex will be. (a) The charge-to-size ratio of the metal ion: a HIGHER charge-to-size ratio produces a MORE stable complex, because a smal…

Metal-ligand bonding in coordination compounds has historically been described by two separate theories, developed to answer slightly different questions.

Valence Bond Theory (VBT) explains complex formation through hybridisation of the metal ion's atomic orbitals.

Two fully worked octahedral examples illustrate how the free ion's spin state changes which orbitals get used in hybridisation.

Worked tetrahedral example: [NiCl4]2-. Nickel's oxidation state in this complex is +2, giving Ni2+ a free-ion valence configuration of 3d8.

Worked square planar example: [Ni(CN)4]2-. Nickel's oxidation state here is again +2, so the free-ion valence configuration is again 3d8.

Valence bond theory, despite its usefulness for predicting a complex's geometry and magnetic behaviour, has three well-recognised limitations.

Crystal Field Theory (CFT) rests on treating each ligand as nothing more than a simple POINT NEGATIVE CHARGE, with the entire metal-ligand interaction assumed to be purely electrostatic (ionic-type) -…

Two separate factors control how large the crystal field splitting parameter, Delta-o, turns out to be for a given octahedral complex.

The splitting of a metal ion's d orbitals into the t2g and eg sets, separated by the energy gap Delta-o, is directly responsible for the colour seen in many octahedral transition-metal complexes.

The pattern of d-orbital splitting predicted by CFT depends on the specific geometry of the surrounding ligand field, and the tetrahedral case gives a splitting pattern that is essentially the OPPOSIT…

Coordination compounds have significant practical importance well beyond the laboratory, spanning biology, medicine, water analysis and industrial metal finishing.

The end-of-chapter questions of this group, exactly as the book prints them.

The end-of-chapter questions of this group, exactly as the book prints them.

The end-of-chapter questions of this group, exactly as the book prints them.

The end-of-chapter questions of this group, exactly as the book prints them.

The chapter's closing hands-on activity, exactly as the book prints it.

Sample papers and previous-year board questions for this subject.