Question

what is the definition of coordination number?

the fraction of the volume of the unit cell occupied by atoms.
the number of nearest neighbors for each atom in a crystalline structure.
the attraction to different particles.
the simplest repeating unit of a crystal structure.

Explanation:

Define coordination number

In solid-state chemistry and crystallography, the coordination number of an atom or ion within a crystal lattice is defined as the number of nearest neighbor atoms or ions in direct contact with it.

Analyze the given options

• Option 1: "The fraction of the volume of the unit cell occupied by atoms." This describes the atomic packing factor (APF).
• Option 2: "The number of nearest neighbors for each atom in a crystalline structure." This matches the definition of coordination number.
• Option 3: "The attraction to different particles." This refers generally to intermolecular or interparticle forces.
• Option 4: "The simplest repeating unit of a crystal structure." This defines a unit cell.

Select the correct option

Based on the analysis, the second option is the correct definition of coordination number.

Answer:

• (A) The fraction of the volume of the unit cell occupied by atoms.
• (B) The number of nearest neighbors for each atom in a crystalline structure. (Correct answer)
• (C) The attraction to different particles.
• (D) The simplest repeating unit of a crystal structure.