Introduction:
Coordination compounds are an integral part of Class 12 Chemistry, featuring prominently in competitive exams and board assessments. These compounds consist of a central metal atom or ion bonded to surrounding ligands through coordinate bonds. Understanding the terms and definitions associated with coordination compounds is essential for mastering this chapter.
In this guide, we will break down critical terms related to coordination compounds into simple, easy-to-remember definitions. This resource will serve as an excellent study aid for students preparing for exams.
Important Definitions in Coordination Compounds:
Coordination Entity:
A coordination entity consists of a central atom or ion surrounded by a fixed number of ligands. For example, [Co(NH₃)₆]³⁺ is a coordination entity where cobalt is the central atom, and NH₃ acts as the ligand.
Ligand:
Ligands are ions or molecules that donate a pair of electrons to the central metal atom/ion, forming a coordinate bond. Examples include Cl⁻, NH₃, and H₂O.
Read Also: Comprehensive Class 12 Chemistry Notes-Lanthanoids and Actinoids
Coordination Number:
The coordination number is the total number of ligand donor atoms bonded directly to the central atom/ion. For example, the coordination number of [Cr(C₂O₄)₃]³⁻ is 6.
Chelation:
Chelation refers to the process by which a ligand forms multiple coordinate bonds with the central atom, creating a ring structure. Ethylenediamine (en) and oxalate ion (C₂O₄²⁻) are common chelating agents.
Central Metal Atom/Ion:
The central metal atom or ion is the species to which ligands are attached. It acts as a Lewis acid by accepting electron pairs from ligands. Example: In [Fe(CN)₆]³⁻, Fe³⁺ is the central ion.
Coordination Sphere:
The coordination sphere includes the central metal atom/ion and the ligands directly bonded to it, enclosed within square brackets. Example: In [Ni(CO)₄], [Ni(CO)₄] is the coordination sphere.
Oxidation State of Central Metal:
The oxidation state of the central metal is the charge it would carry if all the ligands were removed along with their bonding electrons. Example: In [Co(NH₃)₆]³⁺, cobalt has an oxidation state of +3.
Isomerism in Coordination Compounds:
Coordination compounds exhibit isomerism, such as structural isomerism and stereoisomerism. Examples include linkage isomers like [Co(NH₃)₅(NO₂)]²⁺ and [Co(NH₃)₅(ONO)]²⁺.
Conclusion:
Coordination compounds form a fascinating and vital part of inorganic chemistry in Class 12. By thoroughly understanding the definitions of terms like ligands, coordination numbers, chelation, and more, students can confidently tackle exam questions on this topic. These concepts also lay the groundwork for higher-level chemistry studies.
Mastering the terminology is the first step toward excelling in this chapter. With regular practice and revision, students can ace this topic with ease.