Question

Define coordination number.

Hint:

Coordination number counts only sigma bonds between ligands and metal. Pi interactions, if present, are not included in the coordination number.

Answer 1

Step 1: Understanding the term "coordination number."
The coordination number of a central atom in a coordination complex refers to the number of ligand atoms that are directly bonded to the central metal atom or ion. In simpler terms, it is the number of bonds formed between the central metal atom and the surrounding ligands (atoms, ions, or molecules that are bonded to the metal).

Step 2: Determining coordination number.
The coordination number is determined by the number of donor atoms from the ligands that form coordinate bonds with the central metal. It can vary depending on the metal ion and the nature of the ligands involved.
For example, in the complex [Fe(CO)\(_5\)], the coordination number of iron (Fe) is 5, as it is bonded to five carbon monoxide (CO) ligands. In another example, [Ni(NH\(_3\))\(_6\)]\(^{2+}\), the coordination number of nickel (Ni) is 6, as it is bonded to six ammonia (NH\(_3\)) ligands.

Step 3: Conclusion.
The coordination number is crucial in determining the geometry and reactivity of coordination compounds. It influences the shape of the molecule and how the metal interacts with the ligands.

Final Answer: The coordination number is the number of ligand atoms directly bonded to the central metal atom or ion in a coordination complex.