Chemistry Class 12 Chapter 9

Questions and Answers

Which term refers to the charged species surrounding the central metal atom in a coordination compound?

Coordination entity (correct)

Ligand

Ion pair

Chelate

What distinguishes coordination compounds from double salts in terms of their behavior in solution?

Coordination compounds are less stable than double salts.

Coordination compounds retain their identity in solution, while double salts dissociate. (correct)

Coordination compounds contain only neutral molecules.

Coordination compounds dissociate in solution, while double salts do not.

What is the characteristic feature of chelating ligands?

They can only bind to transition metals.

They cause cyclisation around the metal atom. (correct)

They form complex ions with no rings.

They donate only one electron to the central atom.

Which of the following could be classified as a cationic complex entity?

[Pt(NH3)4]2+ Signup and view all the answers

Which type of ligand can bind to a metal atom at more than one site?

Didentate Signup and view all the answers

How does the chelate effect contribute to the stability of coordination compounds?

It leads to less dissociation due to stable ring structures. Signup and view all the answers

What distinguishes geometrical isomers from each other?

They possess different spatial arrangements. Signup and view all the answers

Which of the following is a characteristic of ambidentate ligands?

They can bind through different donor sites. Signup and view all the answers

Which type of complex is formed only with one kind of donor atom?

Homoleptic Complex Signup and view all the answers

In the formula for Effective Atomic Number (EAN), which variable represents the coordination number?

CN Signup and view all the answers

What defines the central atom or ion in a coordination entity?

It is the atom surrounded by ligands. Signup and view all the answers

Which formula represents an octahedral complex that can exhibit cis and trans isomerism?

[MX2L4] Signup and view all the answers

What is defined as the number of coordinate bonds formed by the central metal atom with ligands?

Coordination Number Signup and view all the answers

What type of ligands can form π-bonds and accept electron density from metal atoms?

π-acid Ligands Signup and view all the answers

What does EAN stand for in the context of coordination chemistry?

Effective Atomic Number Signup and view all the answers

Which d-orbitals are classified as t2g orbitals?

dxy, dyz, dzx Signup and view all the answers

Which coordination number typically does NOT show geometrical isomerism?

Coordination number 4 Signup and view all the answers

Which of the following complexes exhibits optical isomerism?

[M(AB)2] Signup and view all the answers

What is called when a complex exhibits slow ligand substitution?

Inert Complex Signup and view all the answers

What do primary valencies in metals correspond to?

Oxidation number of the metal Signup and view all the answers

In tetrahedral complexes, which set of orbitals has a higher energy level?

t2g set of orbitals Signup and view all the answers

How is the oxidation number of the central atom in a complex determined?

By the charge of the complex with ligands removed Signup and view all the answers

What is the condition for the fourth electron to enter an eg orbital in octahedral complexes?

Δo < P Signup and view all the answers

In octahedral complexes of the formula [MA3X3], when three donor atoms occupy adjacent positions, what is this form called?

Facial isomer Signup and view all the answers

What type of orbital splitting is denoted by Δ in a crystal field?

Orbital energy difference Signup and view all the answers

What is the result of optical isomerism in coordination compounds?

Chiral structures that are non-superimposable Signup and view all the answers

In octahedral complexes, how does the energy of the t2g set change relative to eg orbitals?

t2g energy decreases and eg energy increases Signup and view all the answers

Which of the following ligands leads to low spin complexes due to pairing electrons?

Strong field ligands Signup and view all the answers

How are ligands arranged in the spectrochemical series?

By increasing magnitude of crystal field splitting Signup and view all the answers

Which of the following correctly describes the coordination sphere?

The central ion and the ligands attached to it Signup and view all the answers

In a square planar complex of the type [MABXL], how many isomers can be formed?

Three Signup and view all the answers

What defines the crystal field splitting energy in octahedral complexes?

Difference in energies of d-orbitals Signup and view all the answers

What primarily causes the color of coordination compounds?

d-d transitions of electrons Signup and view all the answers

Which statement best describes the relationship between charge on the central metal atom and the stability of coordination complexes?

Greater charge increases stability Signup and view all the answers

Which theory discusses the mixing of atomic orbitals to form molecular orbitals?

Molecular Orbital Theory Signup and view all the answers

What factor does not influence the stability of coordination compounds?

Size of the ligand Signup and view all the answers

What is a limitation of Crystal Field Theory (CFT)?

It does not consider the covalent nature of metal-metal bonds. Signup and view all the answers

Which of the following applications relates to coordination compounds?

Titration methods for estimating water hardness Signup and view all the answers

What is the definition of the stability constant (K) for coordination complexes?

A ratio of dissociated to associated species at equilibrium Signup and view all the answers

In terms of ligand strength, which of the following statements is true?

H2O is a stronger ligand than OH-. Signup and view all the answers

Study Notes

Coordination Compounds

Coordination compounds maintain their identity both in solid and dissolved states.
Central metal atom or ion is linked to surrounding ions or molecules via coordinate bonds.
Example: Potassium ferrocyanide, K₄[Fe(CN)₆].

Double Salts

Double salts are stable in solid form but dissociate into constituent ions when dissolved.
Example: Mohr’s salt, [FeSO₄·(NH₄)₂SO₄·6H₂O], dissociates into Fe²⁺, NH₄⁺, and SO₄²⁻ ions.

Complex Ion (Coordination Entity): Charged species with a central atom/ion surrounded by ions or molecules.
- Cationic complex: Carries a positive charge. Example: [Pt(NH₃)₄]²⁺.
- Anionic complex: Carries a negative charge. Example: [Fe(CN)₆]⁴⁻.
Central Atom/Ion: The atom/ion bound to ligands, often a transition element, referred to as a Lewis acid. Example: Ni in [NiCl₂(H₂O)₄].
Ligands: Electron-donating species (ions/molecules) bound to the central atom.
- Types of ligands:
  - Unidentate: One donor site (e.g., H₂O, NH₃).
  - Didentate: Two donor sites.
  - Polydentate: Multiple donor sites (e.g., [EDTA]⁴⁻).
  - Ambidentate: Monodentate with two possible binding sites (e.g., NO₂⁻, SCN⁻).
  - Chelating: Ligands forming rings around the metal ion, increasing stability via chelate effect.
Coordination Number: Number of coordinate bonds formed by the central metal atom with ligands.
- For monodentate ligands, CN equals number of ligands.
- For polydentate ligands, CN equals number of ligands multiplied by denticity.
Coordination Sphere: The central ion and its attached ligands, enclosed in square brackets; counter ions are outside the brackets.
Coordination Polyhedron: Spatial arrangement of ligands around the central atom.
Oxidation Number: Charge of the complex if all ligands and shared electrons are removed.

Types of Complexes

Homoleptic Complexes: Linked to one type of donor atom (e.g., [Co(NH₃)₆]³⁺).
Heteroleptic Complexes: Linked to multiple types of donor atoms (e.g., [Co(NH₃)₄Cl₂]⁺).
Labile Complexes: Fast ligand substitution.
Inert Complexes: Slow ligand substitution.

Effective Atomic Number (EAN)

Proposed by Sidgwick: EAN of a metal equals total electrons: EAN = Z - ON + 2 × CN
- Z: Atomic number, ON: Oxidation number.

IUPAC Naming of Complex Compounds

Name comprises cation name followed by anion name (e.g., [Co(H₂O)₆]Cl₃).

Stereoisomerism

Different spatial arrangements with the same formula.
- Geometrical Isomerism: cis and trans isomers.
- Occurs in coordination numbers 4 and 6.
- Optical Isomerism: Chiral structures with non-superimposable mirror images (enantiomers).

Bonding in Coordination Compounds

Werner’s Theory: Distinction between primary (oxidation number, satisfied by anions) and secondary valencies (coordinate bonds).
Crystal Field Theory: Describes electron distribution in split d-orbitals in response to ligand approach, creates energy separation.
- Octahedral Complexes: Higher energy in eg orbitals.
- Tetrahedral Complexes: Energy of t₂g > energy of eg.

Colour in Coordination Compounds

Colour results from d-d electron transitions due to ligand interactions.

Limitations of Crystal Field Theory

Fails to account for π bonding in complexes.
Insufficient explanation for ligand strength comparison.

Ligand Field Theory

Integrates atomic orbitals to form molecular orbitals, considering multiple nuclei interactions.

Stability of Coordination Compounds

Stability constant (K) indicates complex stability.
Stability depends on:
- Charge of the central atom (higher charge increases stability).
- Nature of metal ion (stability order: 3d < 4d < 5d).
- Basicity of ligands (strong field ligands yield stable complexes).

Importance and Applications

Used in qualitative and quantitative analysis.
EDTA titrations estimate water hardness.
Metal purification via coordination compounds.
Essential in biological systems.
Catalysts in industrial processes.
Growing interest in medicinal chemistry for chelating therapy.

Organometallic Compounds

Contain metal-carbon bonds; classified into various types.

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Description

This quiz covers key concepts from Chapter 9 of the Chemistry syllabus for class 12, focusing on Coordination Compounds. Explore the characteristics and examples of these compounds, including their stability in different states and the significance of coordinate bonds.