NCERT MCQ Solutions for Class 12 Chemistry Chapter 5 Coordination Compounds

Werner proposed the concept of primary valence (ionisable) and secondary valence (non-ionisable, corresponds to coordination number) for a metal ion.

Werner’s postulates indicate that primary valences are normally ionisable and satisfied by negative ions.

The species within the square bracket (central atom/ion plus ligands) as the coordination entity or complex.

Ligands are defined in the text as the ions or molecules bound to the central atom/ion in the coordination entity. They act as Lewis bases.

A didentate ligand as one that can bind through two donor atoms, giving examples like ethane-1,2-diamine (en) and oxalate (ox).

Ambidentate ligands as having two different donor atoms, citing NO₂⁻ (can bind via N or O) and SCN⁻ (can bind via S or N) as examples.

Ethane-1,2-diamine (en) is a didentate ligand (binds through two donor atoms).
Since there are three ‘en’ ligands, the total number of donor atoms attached to Co is 3 × 2 = 6.

Homoleptic complexes as those where the metal is bound to only one type of donor group, e.g., [Co(NH₃)₆]³⁺.

The cation is named first, whether it is the complex ion or the counter ion.

The IUPAC rules mentioned in the chapter specify that if the complex ion is an anion, the metal’s name ends in -ate (e.g., cobaltate, ferrate).

Stereoisomers as having the same chemical formula and bonds but differing in spatial arrangement. Geometrical and optical isomers are types of stereoisomers.

Geometrical isomerism (cis/trans) using square planar complexes of the type [MX₂L₂] (equivalent to [MA₂B₂]).

Linkage isomerism arises when an ambidentate ligand can coordinate through different donor atoms, as for NO₂⁻ and SCN⁻.

VBT explains bonding as the overlap of filled ligand orbitals (donating electron pairs) with vacant hybrid orbitals of the central metal atom/ion.

Complexes using inner (n−1)d orbitals (d²sp³ hybridization) as inner orbital or low spin or spin paired complexes, e.g., [Co(NH₃)₆]³⁺.

CFT is an electrostatic model assuming the metal-ligand bond to be ionic, arising from electrostatic interactions between the metal ion and point charges/dipoles of ligands.

CFT explains that the e_g orbitals point towards the ligands along the axes and experience more repulsion, thus being raised in energy compared to the t₂g orbitals which lie between the axes.

The spectrochemical series as an arrangement of ligands in order of increasing field strength, which corresponds to the magnitude of crystal field splitting (Δ₀) they cause.

CFT attributes the colour to the absorption of light energy causing electrons to transition between the split d orbitals (t₂g and e_g levels in octahedral fields).

The synergic bonding in metal carbonyls involving sigma donation from CO’s carbon to the metal and pi back-donation from a filled metal d orbital to the antibonding π* orbital of CO.