In crystallography, what do lattice parameters a, b, c and α, β, γ describe?

• A. Lattice site positions
• B. Coordination number
• C. The edges and interaxial angles of the unit cell
• D. Symmetry operations

Answer: (C)

These lattice parameters define the size and shape of the unit cell in a crystal. The three edge lengths a, b, and c set how long each unit cell edge is, while the three angles α, β, and γ specify how those edges meet: α is the angle between b and c, β between a and c, and γ between a and b. Together, they fix the geometry of the repeating unit that tessellates space and determine the cell’s volume. This direct description of the cell’s dimensions is exactly what lattice parameters capture. In contrast, lattice site positions describe where atoms sit inside the cell (their fractional coordinates), the coordination number counts nearest neighbors, and symmetry operations describe the invariances of the lattice—none of these define the cell’s geometry.