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0.30
close-packed direction tetrahedron coordination polyhedron

Rock Salt NaCl

Na⁺ — cation Cl⁻ — anion
6 : 6 coordination · octahedral

Simple Cubic SC

Atoms per unit cell, n1
a–r relationa = 2r
Coordination number6
Close-packed direction
Unit cell volume
APF = 0.524

Atom-sharing study

Click any atom in the 3-D view to make it your reference (drag empty space to rotate). An atom is split between the cells that share it: a cubic corner by 8 cells (⅛), an FCC face by 2 (½), a BCC body-centre by 1; an HCP corner by 6 cells (⅙) and an HCP face by 2 (½).

Derivation