What is the coordination number of the metal in each of the following complexes?
(a) AgCl2-
(b) [Cr(H2O)5Cl]2+
(c) [Co(NCS)4]2-

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1. The coordination number of a metal in a complex is the number of ligands (ions or molecules) directly bonded to it. In other words, it's the number of donor atoms surrounding the central metal atom in a complex ion.

2. For (a) AgCl2-, the coordination number of Ag is 2 because there are two Cl- ions bonded to it.

3. For (b) [Cr(H2O)5Cl]2+, the coordination number of Cr is 6 because there are five H2O molecules and one Cl- ion bonded to it.

4. For (c) [Co(NCS)4]2-, the coordination number of Co is 4 because there are four NCS- ions bonded to it.

5. Remember, the coordination number is not always equal to the oxidation state of the metal. It's about the number of bonds, not the number of electrons transferred.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Coordination Number

The coordination number refers to the number of ligand atoms that are directly bonded to a central metal atom in a coordination complex. It is a crucial concept in coordination chemistry, as it helps determine the geometry and stability of the complex. For example, a coordination number of 4 typically leads to a tetrahedral or square planar geometry.

Ligands

Ligands are ions or molecules that can donate a pair of electrons to a central metal atom, forming coordinate covalent bonds. They can be classified as monodentate (binding through one atom) or polydentate (binding through multiple atoms). Understanding the nature of ligands is essential for determining the coordination number and the overall structure of the complex.

Oxidation State

The oxidation state of a metal in a coordination complex indicates the charge of the metal ion when it is part of the compound. It is important for understanding the electronic configuration and reactivity of the metal. The oxidation state can influence the coordination number, as different oxidation states can stabilize different numbers of ligands around the metal.