Coordination number

Definition

The coordination number is the number of atoms, ions, or molecules that a central atom or ion holds as its nearest neighbors in a complex or lattice structure. It indicates the connectivity and spatial arrangement around the central entity.

5 Must Know Facts For Your Next Test

1. In crystalline solids, the coordination number helps to describe the packing efficiency and density of the structure.
2. For transition metal complexes, common coordination numbers are 4 (tetrahedral or square planar) and 6 (octahedral).
3. The coordination number can influence the physical properties such as melting point, hardness, and solubility of a compound.
4. In ionic compounds like NaCl, each sodium ion has a coordination number of 6 because it is surrounded by six chloride ions in a cubic arrangement.
5. Coordination numbers can vary depending on factors such as ionic size, charge, and the nature of ligands or neighboring atoms.

Review Questions

• What is the significance of the coordination number in determining the structure of crystalline solids?
• How does the coordination number affect the physical properties of transition metal complexes?
• Give an example of a compound with a specific coordination number and explain its arrangement.

Related terms

Ligand:

An ion or molecule that binds to a central metal atom to form a complex.

Lattice Structure: A regular arrangement of particles in three-dimensional space defining crystalline solids.

Octahedral Geometry: A molecular geometry where six ligands are symmetrically arranged around a central atom forming an octahedron.