# Types of unit cells of solid state

$\ce{NaCl}$ forms FCC unit cell but not BCC though $\ce{Na}$ atoms occupy body centre as well as edge centre. Why?

• In NaCl the atom in the center of the unit cell is different than atoms in the corners, so there is no translational symmetry [1/2, 1/2, 1/2] (i.e. no lattice point in the centre of the unit cell), so it's not bcc. – marcin Aug 11 '18 at 21:32