Final answer:
The coordination number of a central metal atom in a complex is determined by the number of coordinate covalent bonds or ligands attached to it within the coordination sphere. Examples include two for [Ag(NH3)2], four for [CuCl4]2−, and six for [Co(H2O)6]2+.
Step-by-step explanation:
The coordination number of a central metal atom in a complex is determined by the number of coordinate covalent bonds to the central metal atom in a complex, or the number of ligands directly attached to it. This number also refers to the number of closest contacts to an atom in a crystalline form.
The coordination sphere of a complex includes the central metal atom or ion plus the attached ligands, which can be observed by the species enclosed within the brackets in a chemical formula.
For example, the coordination number for the silver ion in [Ag(NH3)2] is two, indicating that there are two ammonia ligands attached to the silver ion, with each ammonia molecule donating one pair of electrons to form a coordinate bond.
Similarly, for the copper(II) ion in [CuCl4]2−, the coordination number is four, with four chloride ions attached to copper. Lastly, for the cobalt(II) ion in [Co(H2O)6]2+, the coordination number is six, having six water molecules as ligands.
Ligands can be monodentate, meaning they donate one electron pair to form one coordinate bond, or polydentate (also known as chelating ligands), if they have multiple binding sites. The coordination number is important because it influences the geometry and the properties, including the color, of the compound.